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Walkthrough by daveb

Version: 1.1 | Updated: 01/03/19

                               Doom 4 Walkthrough

   Version 1.1.

                          Acknowledgements and Caveats

   Thanks, id Software for making such a great game!

   Also, watching zomeister's Pistol-Only walkthrough helped me with several
   strategy points. So props to that individual: please watch the madness if
   you want to be inspired: https://www.youtube.com/watch?v=AyVVc0FcS4E

   Caveats: I have not read the "Official" Guide by Prima Guides at this
   point. I may do so soon and amend this guide, as time permits.

                        Introduction and Game Mechanics

Overview

   Welcome to Doom 4, an intense and sensory First Person Shooter!

   The game is set mostly in a large energy facility on Mars, with occasional
   forays into Hell!

   The game is heavy on action and fighting, and it keeps its cut-scenes
   short and punchy.

   The visuals are impressive, contrasting space-tech with organic demons.
   They are also pretty gory: potential nightmare fodder for kids. Even
   though you will plow your way through hundreds of monsters in these
   missions, at least none were human at the time of death.

Basic Plot Summary

   You awaken to being chained to a bed, and quickly assume the hero's role:
   combatting an experiment with Hell gone awry. Over the missions, you'll
   see that cutting-edge research into new energy sources degenerated into
   cultish madness, including ritualistic sacrifices. It's up to you to stop
   the unleashed demons.

Controls

   PS 4        X-Box             Description                                 
   L1          LB                Use equipment (usually Grenade)             
   L2          LT                Weapon Modifier (meaning depends on weapon) 
   R1          RB                Switch or Select Weapon                     
   R2          RT                Fire Weapon                                 
   R3          Press Right Stick Melee Attack / Glory Kill                   
   Square      X                 Chainsaw                                    
   Triangle    Y                 BFG                                         
   Circle      B                 Crouch / Stand (toggle)                     
   X           A                 Jump                                        
   Up Arrow    DPad Up           Swap Weapon Mod                             
   Left Arrow  DPad Left         Previous Equipment                          
   Right Arrow DPad Right        Next Equipment                              
   Down Arrow  DPad Down         Mission Objective Summary                   

Weapons

  Pistol

   What the Pistol lacks in power it makes up for by having unlimited ammo.

   The lack of power can be an advantage if you are trying to stun a demon in
   order to Glory Kill it, if you are trying to extract more stuff from the
   kill.

   My upgrade strategy: save the upgrades for the end, or maybe induldge in
   the first 1 point upgrade. There are more important ways to spend one's
   upgrade points.

  Shotgun (available Mission 0)

   Although the shotgun is eclipsed by the Super Shotgun (which is much
   better, once upgraded), you'll have no real choice for the first few
   missions. Because of this, it isn't really worth putting Weapon Upgrade
   points into the shotgun, at least not until later in the game if you are
   trying to get 100%.

   When you get to the first Field Drone, the Shotgun is the only weapon you
   have to modify, so you have to get a mod at this early point: go for
   Explosive Shot, which is easier to use to get the "Twofer" Challenge (for
   Mission 2).

   Cyber-Mancubi count as Mancubi for the Changed Shot Upgrade Challenge.

   (Technically, the game refers to this weapon as the "Combat Shotgun", but
   nobody calls it that.)

  Plasma Gun (available Mission 2)

   Although it's individual shots are rather weak, it fires quite rapidly.

   More importantly, Heat Blast is a really powerful Weapon Modification.
   Basically, it allows you to kill everything near you at the same time
   without using ammo, BUT it requires you to shoot the gun to charge up the
   blast. There are 2-4 places you can use the Heat Blast and Quad Damage
   Powerup to really plow through large numbers of demons.

   I haven't found the Stun modification to be very useful: it wastes ammo,
   it's hard to stun more than 2 demons, they don't stay stunned long, and
   you still have to kill them (taking both time and ammo usually).

  Assault Rifle (available Mission 2)

   Each individual shot from the Assault Rifle is rather weak and becomes
   weaker and harder to hit from a difference. Few demons can be killed with
   a single shot; expect a cacodaemoon (etc) to take 30+ shots even up close.

   ihe Tactical Scope changes things a bit: it makes the thing pretty
   effective for sniping, and the upgrades make it pretty damaging. Even so,
   it's a bit tedious killing things with this weapon.
   However, it makes for a nice change, since the opportunities for sniping
   are few in this game. You can usually get the challenge upgrade naturally
   over the course of the game, but you can also replay an earlier mission to
   get it pretty easily.

   The Mini-Missiles seems like a cool upgrade but they aren't that powerful
   or predictable. One nice use is for dealing with multiple Lost Souls. Most
   other monsters are too strong for this to be an elegant attack.

  Super Shotgun (available Mission 4)

   A weapon big enough that it'll at least distract anything. Fully upgraded,
   it's my weapon of choice for Hell Knights, or combats with a long chain of
   individual demos.

   The challenge upgrade can be a bit difficult: I usually get very close to
   one demon and shoot through it to get to another one close behind; this
   seems easier than lining them up side-to-side.

  Chain Gun (available Mission 6)

   A powerful weapon that is a bit annoying to use because it takes a a few
   seconds to start up.

   The Gattling Rotator works, but you have to hold down the modifications
   button the entire time: I don't really like that.

   The Mobile Turret mod is a great way to deliver a lot of damage. I usually
   try to fully upgrade this modification since it's useful against bosses.

  Gauss Cannon (available Mission 5)

   The most powerful standard weapon, even without mods. Siege Mode is the
   most powerful mod (by far), and it is strongly recommended. Its challenge
   upgrade is easy too.

   The Precision Bolt mod is also pretty good but it's a lot harder to fully
   upgrade and only kills once thing at a time, so I seldom use it.

  BFG (available Mission 8)

   The Big F-ing Gun. This will clear out a whole room of demons, but it can
   be a little unpredictable in how it works.

   Ammo is found individually, and you always have a limit of 3. However, the
   Ammo Boost II rune WILL cause enemies to randomly drop BFG ammo when they
   die so there isn't too much of a shortage.

  Chainsaw (available Mission 2)

   This crazy melee weapon will definitely kill any monster (except Bosses)
   in range that you have enough fuel to kill. The initial capacity is 3 Fuel
   Units, which is the amount in every gas can. Each Argent Cell upgrade to
   the Ammo Capacity increases your capacity by 1 Fuel. So fully upgraded,
   you have a capacity of 7 Fuel Units.

   Killing with a chainsaw is considered a Glory Kill that'll dump a huge
   pile of ammo.

   Fuel to kill various demons:

     * Imp: 1
     * The Possessed: 1
     * Unwilling: 1
     * Possessed Guard: 1
     * Possessed Securities: 1
     * Hell Razer: 1
     * Hell Knight: 3
     * Summoner: 3
     * Cacodaemon: 3
     * Pinkie: 3
     * Spectre: 3
     * Revenant: 3
     * Mancubus: 5
     * Cyber-Mancubus: 5
     * Hell Baron: 5

  Weapon Upgrade Path: In My Humble Opinion

   Here's how I upgrade my weapons. I usually upgrade one-at-a-time, simply
   because that spaces the Upgrade Challenges out more.

     * Plasma Rifle / Heat Blast
     * Rocket Launcher / Lock-On
     * Super Shotgun
     * Gauss Cannon / Siege Mode
     * Assault Rifle / Tactical Scope (Often I get the first two upgrades
       before Siege Mode is available)
     * Pistol
     * Rocket Launcher / Remote-Detonation

Monsters

  The Possessed, Unwilling

   These idiots simply stagger around, vaguely coming toward you.

   In Nightmare mode, they do quite a bit of damage; in easier modes they are
   merely pesky.

  Imps

   Monkeys with fireballs with great aim. You have to move constantly and
   keep a lookout to avoid getting hit.

   They can take a fairly large amount of damage when they are climbing
   around on vertical surfaces.

   For players in Nightmare mode, Imps will probably cause more deaths than
   any other demon.

Possessed Engineers

   Somewhat like the Possessed, except they explode when they die, and they
   charge at you to cause trouble.

   These guys are walking bombs - typically when they die they'll fly away
   from you which mitigates the problems. But some weapons might cause them
   to fly at you, and they'll do moderate damage.

   Even if you jump from above them and Glory Kill them, it does not count as
   a Death From Above Glory Kill (at least for the purposes of Rune or Combat
   Challenges). I'm assuming they their firey plume keeps them safe ? TODO:
   read the damn codex on this

  Possessed Soldiers and Possessed Securities

   These two monsters differ in that the latter has shields.

   They have 3 attacks:

     * Plasma Volley: an attack of many straight-moving weak plasma baubles
     * Plasma Grenade: a stronger attack, similar to the Rocket Launcher /
       Remote Detonation. It expands before blowing up like a bomb.
     * Melee Attack: these are fairly weak for Possessed Soldiers, but they
       are quite strong from the shielded soldiers

   The shields are a big difficulty: the Gauss Cannon or Chainsaw are the
   surest ways to kill them - you'll run into them before you have the Gauss
   Cannon. Otherwise, try running around them (around a structure) or jumping
   over them. Also they have to put their shields down when the jump/drop.

  Hell Razers

   These hellions attack with a laser in their arm, or a melee attack.

   They have a lot of hit-points, but they aren't too hard to kill.

  Lost Souls

   These little punks are very damaging.

   It's best to snipe them from afar (effective weapons: Assault
   Rifle/Tacticle Scope, Rocket Launcher/Lock-On, BFG). At the last moment
   when they are swooping in on you, the Shotgun or Super-Shotgun is probably
   the best, if you're quick.

   They can make little turns, but you can sneak behind pillars or protected
   areas.

  Hell Knights

   These are brutal melee attackers.

   They will jump toward you very fast.

   It is best to approach them right after an attack (Super Shotgun, Gauss
   Cannon) then back-off - a kind-of dance, or just use the Chainsaw which'll
   definitely kill them if you have fuel.

  Summoners

   These red-dressed ladies fire intense energy beams along the floor.
   Fortunately, the shot comes with a harmless pre-shot, so if you see a
   short red flame running along the ground, get away from it.

   The Rocket Launcher / Lock-On's Multi-Target Upgrade requires 5 kills on
   Summoners, so if you want to get that upgrade, you'll want to kill every
   summoner with lock-on rockets. That said, this upgrade isn't particularly
   useful.

  Cacodemons

   Big floating eyeballs with gigantic purple missiles.

   They do (as a hint notes) have a weak point near their eye opening, and
   precision shots with the tactical shot of the assault rifle can kill it
   from afar pretty quickly.

  Revenants

   These tough lanky flying demons wear a backpack to shoot you from above.
   They can take a significant amount of damage.

   The visible patch on the sternum (center of the chest) is a weak point.

  Pinkies and Spectres

   These are big charging idiot monsters. The Pinkies are substantially
   heartier. They are literally pink. The Spectres are essentially camoflaged
   Pinkies. They blend into their surroundings.

   I suggest using Super Shotgun, Chainsaw, Gauss Cannon on these guys. But
   really, any weapon will work.

   Their tail/backside is their weakness. A single point-blank Super Shotgun
   blast to the base of the tail will usually kill it. (Two such shots
   definitely will, but most of the time the Pinky will start moving before
   you can get a second shot)

  Mancubi and Cyber-Mancubi

   These large (obese) demons shoot damaging fireballs. The Cyber-Mancubi are
   somewhat more annoying because their shots leave a toxic (green) residue
   that you must avoid (it only lasts a few seconds).

   The visible patch on the sternum (center of the chest) is a weak point.

  Hell Barons

   These are like Hell Knights except that they can shoot missiles. With
   horns.

   They are really not that tough, because they can be taken down by 2 Gauss
   Cannon / Siege Mode shots.

Equipment

   Generally speaking, most players use mostly one type of Equipment: the
   Frag Grenade. It is effective, you get it early on, and it is easy to
   understand.

   The Siphon Grenade is substantially harder to aim, and less damaging, so
   it isn't used too much.

   The Hologram (sometimes called the Decoy) seems like a good idea, but I
   really haven't found places I personally like to use it.

   Contact me if you have suggestions for Siphon Grenades or Holograms!

  Frag Grenades

   These have both good radius and damage and are recommended. I know that as
   a beginner, I under-used them. One problem is that they take a long time
   to regenerate until you get the first Praetor Suit Equipment Upgrade.

  Siphon Grenades

   These pull energy from demons in their radius and give it to you. But the
   amount transferred isn't that great, so it tends to be overlooked.

Level Overview

   Mission                Subtitle   Elite  Argent Field  Rune   Secrets Data 
                                     Guards Cells  Drones Trials         Logs 
   Mission 1: The UAC     Rip and    1      0      1      0      3       2    
                          Tear       
   Mission 2: Resource    Know Your  3      1      1      0      8       2    
   Operations             Enemy      
   Mission 3: Foundry     Meltdown   3      1      1      0      6       3    
   Mission 4: Argent      Beginning  4      1      2      2      5       4    
   Facility               of the End 
   Mission 5: Argent      Argent     3      2      1      2      7       4    
   Energy Tower           Tower      
   Mission 6: Kadingir    Into the   4      1      1      2      6       7    
   Sanctum                Fire       
   Mission 7: Argent      Hell on    4      1      1      2      6       5    
   Facility (Destroyed)   Mars       
   Mission 8: Advanced    A Brighter 3      2      1      2      10      4    
   Resource Complex       Tomorrow   
   Mission 9: Lazarus     Lazarus    4      1      1      2      9       5    
   Labs                   
   Mission 10: Titan's    Titan's    2      1      1      0      6       4    
   Realm                  Realm      
   Mission 11: The        The        2      1      1      0      3       3    
   Necropolis             Crucible   
   Mission 12: VEGA       I am VEGA  3      0      0      0      5       4    
   Central Processing     
   Mission 13: Argent     The Well   0      0      0      0      5       0    
   D'Nur                  

Weapon Upgrade Tokens

   You spend these to improve your weapons:

   Weapon          Upgrades                      Upgrade Points Required For  
                                                 All Mods                     
   Assault Right   Tactical Scope, Mini Missiles 18                           
   Combat Shotgun  Charged Shot, Explosive Shot  18                           
   Plasma Rifle    Heat Blast, Stun Gun          18                           
   Chain Gun       Gattling Revolver, Mobile     18                           
                   Turret                        
   Gauss Cannon    Precision Bolt, Siege Mode    18                           
   Rocket Launcher Lock-On, Remote Detonation    18                           
   Super Shotgun   -                             9                            
   Pistol          -                             9                            
   Total                                         126                          

   You earn Weapon Upgrade Tokens as follows:

   Mission     Exploration Challenges Combat Bonus Bosses Total Cumulative 
   1: The UAC  2           0          0      0     0      2     2          
   2: Resource 2           3          0      0     0      5     7          
   Operations  
   3: Foundry  2           3          5      0     0      10    17         
   4: Argent   2           3          5      0     0      0     10         27 
   Facility    
   5: Argent                                                               
   Energy      2           3          5      0     0      10    37
   Tower       
   6: Kadingir 2           3          5      0     0      10    47         
   Sanctum     
   7: Argent                                                               
   Facility    2           3          5      0     0      10    57
   (Destroyed) 
   8: Advanced                                                             
   Resource    2           3          5      0     0      10    67
   Complex     
   9: Lazarus  2           3          5      2     6      18    85         
   Labs        
   10: Titan's 2           3          5      0     0      10    95         
   Realm       
   11: The     2           3          5      0     6      16    111        
   Necropolis  
   12: VEGA                                                                
   Central     2           3          5      5     0      15    126
   Processing  
   13: Argent  2           3          5      0     6      16    142        
   D'Nur       

   So, if you 100% the game you should have 142 - 126 = 16 unusable Weapon
   Upgrade points at the end. Another way to look at it: there are 16 extra
   Weapon Upgrades Points.

   That said, the extra combat upgrades have to be earned, so earning 100% on
   one playthough (ie without taking advantage of Mission Replay or dying),
   is logistically tricky, if not impossible.

Checkpoints

   Checkpoints save your ammo, health and armor levels, as well as the
   locations of pickups of the same nature.

   On the other hand, Secrets, Argent Cells, and Elite Guards are all saved
   without making a checkpoint.

   This system usually works quite well, but the Argent Cells have a
   side-effect of filling up whatever power you upgrade. This isn't saved
   unless you find a checkpoint elsewhere. This rarely comes up besides in
   Mission 7 where we provide some advice.

  Checkpoints, in Summary

   Things that are captured immediately:

     * Secrets, Argent Cell, Elite Guard usage

   Things that are preserved by checkpoints:

     * demon kills
     * pickups (except those dropped by demons)
     * Health, Armor and Ammo levels

   Things that are lost by dying after a checkpoint:

     * the fill-up delivered by Argent Cells
     * partial (pending) powerups at the time of the checkpoint

Your Dossier

   These are accessed by the central button on PS4.

   These pages are introduced pretty well described by in-game tutorials, so
   I'm not going to repeat all that information.

     * When you get an Auto-Map, the effect is to enhance the map in your
       Dossier. Praetor Suit upgrades can improve the map in various ways
     * Weapons and Praetor Suit Upgrades are explained over the first few
       Missions
     * Tutorial Codex pages are automatically added to the Codex page.
     * The Codex page will let you see if you have missed any Codex Entries

Navigation

   Your dossier has a 3-d map that is pretty nice, but it doesn't give a
   coordinate system, nor labels for places, nor even a reference direction,
   like North. It does provide some icons that can be used as landmarks.

   Fortunately, almost every location in this game looks somewhat different,
   so it's not so bad. But pay attention to the names given to certain major
   rooms/locations, since usually if i give it a name, then you'll arrive
   there a few times.

Difficulty Levels

   Based on my own experience (and I could be wrong):

     * difficulty levels affect:
          * damage done by demons
          * gains from ammo, armor, and healh pickups
          * runes: Rich Get Richer
     * difficulty levels do not affect:
          * number or placement of demons
          * chainsaw
          * secrets (except the size of an Armor pickup)
          * runes: In-Flight Mobility
     * i'm not sure if these are affected:
          * health of monsters
          * damage of user's weapons
          * environmental damage to the user
          * environmental damage to the demons

   Ultra-Nightmare is the same as Nightmare for this information.

Runes

   I provide hints about how to complete the Runes Challenges where you come
   across them. These are hints about when to use runes, and how to upgrade
   them (as easily as possible- both on a single playthrough as well as using
   Mission Replay).

  Vacuum

   Easy to get and the most important rune. Upgrading is easy as well - jump
   make sure to remember to equip it after you complete the challenge (it
   won't remind you in nightmare mode).

  Dazed and Confused

   This rune comes in handy for the Bosses at the end of Mission 11, and for
   fulfulling the Combat Challenge "To Be Knighted" for Mission 4: without
   the Jump Boots, Death From Above Glory Kills on Hell Knights can require
   some setup.

  Ammo Boost

   Very useful: I have this on much of the time.

  Equipment Power

   This will make your grenades pretty powerful, and is basically trivial to
   upgrade (just throw 30 grenades with the rune enabled). If you upgrade
   your Equipment Power using Praetor Tokens, it'll make grenade throwing
   faster, and hence make the upgrade easier to get and more powerful.

  Seek and Destroy

   Useful for most berserk powerups - and those are great times for upgrades.

  Savagery

   Useful for most berserk powerups.

  In-Flight Mobility

   This rune is almost vital for the last boss fight - and the upgrade is
   pretty critical too.

   It might make sense to work on this upgrade at the same time as the Dazed
   and Confused upgrade.

   Challenge tips: there is very little room for error. You must single jump
   across the split every time - if you double-jump (which is tempting,
   because the separation is pretty wide for a single-jump), it'll waste
   valuable time. The crux is probably hitting the annoying mid-air relic in
   the second half of this course, but note that you have two chances at it,
   since you have to jump left-to-right then right-to-left in that area.
   Obviously most people aim to get it in the first jump, but it's good to
   keep cool if you miss it on the first jump since you have another chance.

   Upgrade notes: You need to get 25 Mid-Air kills. Note that "Mid-Air"
   refers to you, not the demon. As a result, glory-kills from above are
   probably the easiest way to get this, so it makes sense to try to combine
   this upgrade with the Dazed and Confused upgrade.

  Armored Offensive

   Very useful, easy to upgrade, just keep it on a lot. Also, the upgrade is
   measured it armor points you pick up. In particular, picking up a
   Mega-Health will contribute 200 points for this upgrade.

  Blood-Fueled

   Useful during Berserk Powerups - this is also a good time to get the
   upgrade.

  Intimacy is Best

   There's only one place this upgrade is helpful (unless you count mission
   replay): the Atop the Mountain challenge in Mission 10.

   Upgrade hint: although you might think this would be efficient to get in
   conjunction with the various glory-kill upgrades, it's probably best to
   upgrade this by finding a group of The Possesseds and staggering them over
   and over again with the pistol. It only takes about a minute or so.

  Rich Get Richer

   This is quite useful in several Argent D'Nur fights.

   To upgrade this, you need 12 Armor Fillups. An Argent Cell counts, as do
   Mega-Healths. But you'll struggle to get about 6 of those. One options is
   to use Toxic-Sludge to do a single point of damage -- Unfortunately
   there's really only one fight [Mission 10, Pounding Rock Area] that has
   easy access.

   Upgrade hint: in Nightmare mode, getting up to full Armor is difficult,
   except when the Mega-Health powerup. If you don't mind dying multiple
   times, there are a few Mega-Healths you can use to get the upgrade. you
   can die and multiply get several Mega-Health, Toxic Sludge is a convenient
   way to drop just a single health at a time.

  Saving Throw

   A possibly useful safeguard in Ultra-Nightmare or Arcade Mode, but in
   casual play for campaign mode, not too useful.

                  Mission-by-Mission Plot Summary (SPOILERS!)

   For the most part, the plot in this game isn't very important. But I
   wanted to summarize the whole plot briefly so casual players can refresh
   their memories.

   Before any mission, you, Doomguy, are awoken from your slumber. You learn
   in a cut-scene that a satellite must be realigned to learn the status of
   the complex: THE UAC (Mission 1) (abbrev for Union Aerospace Complex).
   First you must gain access to the .... From there, you are taken to
   RESOURCE OPERATIONS (Mission 2): first half of mission is to realign the
   satellite (merely requires getting to a particular terminal). The second
   half of the mission is to get to a VEGA Terminal, where you learn the
   extent of the catastrophe.

   The discussion is interrupted by news of an emergency in THE FOUNDRY
   (Mission 3). At the end of Mission 3, you learn Olivia Pierce is the
   source of the disruption, and that she's headed for a hugely concentrated
   argent beam. The first plan of attack is to disable the filters that feed
   argent energy to the tower in the ARGENT FACILITY (Mission 4). But, of
   course, it turns out that the Tower is still dangerous, and you have to
   get up there to try to disable it.

   Before climbing the ARGENT ENERGY TOWER (Mission 5), you have to get to
   it, which involves of a lot of jumping around on catwalks (what I call
   "The Bridge"). Getting up is similar. Ultimately, Olivia beats you to it,
   and the portal is opened.

   After that, the missions have a general arc: trying to close a portal to
   hell.

   The force of the portal opening transports you into hell. This area of
   hell is known as KADINGAR SACTUM (Mission 6): where you were excavated
   from. Somehow, they set up a portal at the end of the mission that returns
   you to the ARGENT FACILITY (DESTROYED) (Mission 7).

   This time, you are here to catch a tram to the ADVANCED RESEARCH COMPLEX
   (Mission 8). You'll finally meet Dr Samual Hayden. Then you'll go to the
   weapons division, LAZARUS LABS (Mission 9). This level concludes in a boss
   fight, in two parts. Part 1: you fight the demon on Mars and rip out the
   argent accumulator, which sends you back to hell. Part 2: in Hell, ...
   TODO

   TITAN'S REALM (Mission 10).

   NECROPOLIS (Mission 11).

   VEGA CENTRAL PROCESSION (Mission 12).

   ARGENT D'NUR (Mission 13).

                                Using this Guide

   Secrets, Field Drones, Argent Cells, Rune Challenges are all written in
   uppercase at their secret location, with dotted notation where the first
   number is the mission and the secret is the index of the location in the
   Dossier Overview/Map page. For example, SECRET 14.3 would be the third
   secret in the dossier in mission 14 (but there's really only 13 missions).
   This is intended to facilitate searching.

   As a perhaps dubious consistency I will use all-caps the first time you
   meet a monster or can collect a weapon. Subsequently, I will use title
   case.

   (In the case of monsters, there are two grammatically annoying ones: The
   Possessed and Possessed Security. I'm just going use them like they were
   real nouns, and i'll therefore pluralize them as The Possesseds and
   Possessed Securities.)

   I will use title case (ie first letters capitalized) for various other
   collectibles: Suit of Armor, Small Armor, Health Station, Mega-Health,
   etc.

   Similarly CHECKPOINT is always written uppercase to indicate that the game
   will give a checkpoint. The significance of that is that it is nice to
   load up on supplies right before getting the checkpoint. (So that if you
   die, you won't have to get the supplies again)

                                About this Guide

   This is the first Walkthrough that I (Dave Benson) have written. I hope
   you find it useful.

   I am no expert game player. I just really like this game, and decided to
   write a walkthrough since the one like I wanted didn't exist.

   I found it to be an interesting challenge, mostly due to the difficulty of
   describing locations.

   I welcome contributions, compliments, suggestions, errata, strategies,
   complaints, and donations. Contact me via github for details, or submit
   bug reports:

     https://github.com/davebenson/doom4-walkthrough

                               Mission 0: Pre-UAC

   At the beginning of the game, you wake up chained to an operating table.
   As you break out of your bonds, four demons surround you, your first
   encounter with THE POSSESSED.

   Before you have control, you kill one by hand, and grab a pistol.

   Shoot the remaining three.

   Interact with the screen (to the right of the door) and proceed into the
   central room with the Praetor Suit. Interact with it, and meet Dr Hayden.

   Ultra-Nightmare skips the Mission 0 fights.

Mission 0: Mini-Fight 0.1: Glory Kill Tutorial

   You will come upon a staggered The Possessed. After killing it, kill the
   remaining 4 weaklings.

Mission 0: Mini-Fight 0.2: Meet the Imp

   Interact with a corpse to get the SHOTGUN.

   Enter the next room.

   A quick cut-scene will play as the IMP scurries down from the rafters.
   Kill it, obviously (using the Shotgun).

Mission 0: Fight 0.3: Blue Elevator Chamber

   You exit the anteroom to see 8? The Possessed worshipping an Orb. You can
   Glory Kill them if you need health or kill them en masse by shooting the
   barrel.

   After destroying the Orb, about 15? Imps will gradually materialize. Keep
   moving! There are two sheltered areas: the entrance area, and a
   control-room overlooking the main chamber.

   Grab all stray stuff before entering the elevator. CHECKPOINT.

                       Mission 1: The UAC "Rip and Tear"

Mission 1: Intro

   The mission starts with you exiting an elevator, and dropping onto a lower
   plane. 3 small armor pieces are there; proceed upward to find CODEX ENTRY
   "Environments / The UAC".

   As you approach another tall cliff, you can see Imps running off into the
   horizon: these can be shot but it's not worth the effort. You can also
   shoot The Possesseds below, but it's better to use them as walking health
   bonuses.

Mission 1: Fight 1.1: Pre-Blue-Keycard

   This is the first real fight of the game. It occurs on a 2-level
   dual-figure-eight structure.

   If you are quick and accurate, you can target some imps on the cliffs
   above, and you can shoot at The Possesseds below. In my opinion, these
   aren't worth spending time on.

   Like many fights throughout the game, you will learn your own opening
   gambit. For me, I target the 2 POSSESSED SOLDIERS that appear right in
   front of you: one in the center in front of a pinnacle, and one at right
   near a barrel that can be shot. After that, just keep moving and shooting.

   You'll be able to recharge over the next easy fight, so use up all the
   health and armor during the fight.

Mission 1: Keycard and Secret

   After the demonic threat is neutralized, a gate opens up, opposite the
   entrance location. However, another gate immediately (requiring the Blue
   Keycard) blocks progress. Turn right and walk down a tunnel. Behind a
   large block is a corpse with a Blue Keycard.

   After getting the keycard, stand on the block and look around for a tunnel
   above you. You should jump to it, and pick up SECRET 1.1 and your first
   collectible, COLLECTIBLE 1.1 "Combat Shotgun Model, Blueguy".

   Continuing through the tunnel, you'll get to the gate, which will open.

   You'll get some ammo, but more importantly, the FRAG GRENADE, which is
   very useful, especially once your suit's equipment upgrades are done.

Mission 1: Mini-Fight 1.2: Stray Possessed and Imps

   There's about 6 The Possesseds and 3 Imps.

   After killing those guys, enter the cave to the right (at the top of the
   incline). You will find some worshipping Possessed and an Auto-map.
   Continue out the cave to find a Praetor Token (ELITE GUARD 1.1) on the
   right before jumping down.

Mission 1: Mini-Fight 1.3: Stray Imps

   As you drop down the last level of this spit of land, 5 Imps will attack
   from various directions.

   CHECKPOINT.

   After that, look for the large tank with TRI 9-C printed on it, and enter
   its lower level. There is a lever through that you should interact with
   then enter the Classic Doom Level. Exit the structure and you should be
   able to see up the path to SECRET 1.2, CLASSIC MAP 1.1 "Doom II:
   Entryway".

Mission 1: Classic Fight 1.4: Classic Doom Level

   There are 4 Possessed Soldiers standing on pedestals in here. I usually
   use a Frag Grenade to kill the left one, then snipe the right one from
   just under the pillar. The remaining two can be taken out one-at-a-time.

   If you actuate the switch nearer the entrance, you can get some minor
   booty. Mostly, this fight isn't worth the effort.

   After this, jump onto the crates at the end of the landing bay, and jump
   the chasm.

   At the end of this area, you may catch a glance of the Field Drone flying
   away to the right. But go left to an area with Health and Armor, and the
   second CODEX ENTRY "Environments / The UAC".

Mission 1: Fight 1.5: Just Across the Chasm

   Go back, and to the right where you saw the Field Drone; it's floating
   right ahead. Interact with it: I tend to get Charged Shot as it makes an
   upcoming challenge easier, but either (or none) can be used.

   You will come across some The Possesseds worshipping a corpse. There are 3
   Possessed Soldiers around in the peripheries as well, and they will be
   join in the fun by some Imps that'll spawn, potentially close to you.

   After killing them, CHECKPOINT.

Mission 1: Fight 1.6: Pre Entranceway Area

   This canyon can be approached in two ways:

     * go directly up the canyon
     * back up and ascend some cliffs to the left (there's a Medium Health
       visible), cross over the canyon on a land bridge, then turn left and
       climb up a yellow metal wall.

   Either way, expect 5+ Imps (plus some The Possesseds).

   CHECKPOINT.

   You should see a suit of Armor on a small plateau. Just before that, at
   the canyon's bottom, look around for a small backfacing greenlit "secret"
   tunnel. It leads to a cliff with SECRET 1.3 to COLLECTIBLE 1.2 "Imp Model,
   Classicguy".

Mission 1: Fight 1.7: Station Entrance

   You can approach this fight up the main road (over the plateau with a suit
   of armor), or from the side using the plateau to the right. Use grenades
   to knock these forces back, and retreat to snipe at the various demons.

   It's about 6? Possessed Soldier, 6? Imps, and 12? The Possessed.

   Search all over for ammo.

   Now, go up to the top level. You'll see a medium Health. And at the end of
   both of the broken tracks there are carts containing Health and Ammo.

   Enter into either of the twin doors, there's some armor - pick it up if
   needed, then proceed to the waypoint.

                Mission 2: Resource Operations "Know Your Enemy"

Mission 2: Notes on Combat Challenges

     * Two-fer: This is easy with the Explosive Shot: use the Weapons Mod key
       and shoot a Possessed that is in close range of another Possessed. Or
       stagger one in order to line them up carefully. It can be done without
       weapon mods by staggering two Possessed and getting really close to
       one and shooting through it to the other staggered being.
     * Variety is the Spice of Death I: perform 5 different Glory Kills on
       the Possessed. There's a lot of options; use the Pistol (instead of
       Shotgun) to more reliably stagger (as opposed to kill) them.
     * Quite the Explorer: Find 3 Secrets. This should be pretty easy, with
       this guide.

Mission 2: Mini Fight 2.1: Before opening hatch

   5 Possessed wait here, and 2 Imps spawn quickly. Kill the Imps and use the
   Possesseds to work on either Challenge "Variety is the Spice of Death I"
   or "Twofer" (this is easiest using the Explosive Shot modification).

   You can't open the hatch yet: "Low Power". Instead, open a door to find a
   number of The Possessed, and keep going to an Imp at the top of the
   stairs. "Reset Power" (by interacting with a screen), to watch a bit of a
   cut-scene featuring an Olivia Pierce recording.

   Looking down at the stairs from the top, you should see a platform at your
   level with a blood smear on the back wall: a standard marker for a secret
   in this game. Go there, and look for some ducts to climb through. You'll
   get to SECRET 2.1 and a suit of armor.

   Back at the bottom of those steps, find an Auto-Map: use it.

   Continue to the waypoint and an Open the Maintenance Bay Door.

Mission 2: Mini Fight 2.2: Tiny fight in catwalk area with Original Doom Level

   Some Possessed are followed by 3 Imps. Go where they originated onto a
   crane-like catwalk. Jump over its left railing, and look for a platform
   somewhat above you: jump to it. Look for the Lever and pull it.

   Jump back down, keeping an eye out for some Imps that'll spawn right
   around you. You should see the SECRET 2.8, CLASSIC MAP 2.1 "Doom - Hangar"
   up a small staircase with some Health and Shotgun ammo.

   After that, open the door with the waypoint to meet the Possessed
   Engineer. Shoot him and he'll fly back, killing the numerous Possesseds in
   the background.

   A battle awaits after opening the next door.

Mission 2: Fight 2.3: U-shaped catwalk area

   This can be a difficult fight, but judicious use of Grenades, Barrels, and
   Possessed Engineers can make it fairly painless.

   Post Fight: There's CODEX ENTRY "Environments / Resource Operations" and a
   door.

   You can enter the room through a path with more goodies by looking for a
   screen in the left of the control console that you can interact to "???".
   This will stop the fast moving elevators at the central part of the U.
   Climb up the elevators and enter through the second story for health,
   armor, and shotgun ammo.

   No matter which way you go, you'll be in a locker room with some Shotgun
   Ammo, the Chainsaw, and a Health Station.

Mission 2: Fight 2.4: Industrial Train Depot

   A long hallway fight, with a bit of a side-corridor at the end.

   You can fight it from the entrance gate, or you can charge in. There's a
   few barrels that you can shoot to good effect; grenades are also helpful
   here, as can be the chainsaw.

   ??? CHECKPOINT.

Mission 2: Getting the yellow keycard

   Cross the train-tracks on the far-side of the room from your entrance. You
   will see a gas canister across the tracks. Turn left and carefully go
   through the hatch which automatically opens and closes. It is an elevator.
   When the door opens on the upper level, there should be a large armor.
   Take it and go forward. There should be a train on the left leading back
   to the Industrial Train Depot, and on the right is a Security Station.

   Drop drop and take out the few The Possesseds.

Mission 2: Mini Fight 2.5: In front of Security Station

   4 The Possesseds.

   Load up on health and armor before proceeding, since the next fight can be
   tough.

   Since you don't have the Yellow Keycard yet, you will have to go down the
   hall to a developed outdoor area.

   CHECKPOINT.

Mission 2: Fight 2.6: Developed Outdoor Gore Nest

   Before destroying the gore nest, take out the 6? The Possesseds possibly
   using Glory Kills to get more health. I tend to use the pistol to save
   ammo.

   After destroying the Gore Nest, a large number of Imps and Possessed
   Soldiers appear, keep moving and shoot the barrels to kill some of them
   while saving ammo. Make note of the two supply caches containing
   ammo+health before starting.

   Hint: The chainsaw is useful here to kill 3 demons and get lots of ammo.

Mission 2: Getting the yellow keycard (continued)

   On the lower level, Call the Elevator and see a replayed cut-scene of the
   demon carrying the Yellow Keycard guard. Enter the elevator and press the
   button.

   On a catwalk area you'll find some health, FIELD DRONE 2.1, shotgun ammo
   and the corpse of the Yellow Keycard guard. I recommend waiting to use the
   field drone until you have the Plasma Rifle. Take the Yellow Keycard and
   watch out!

   Go through the hatch then drop down into the Industrial Train Depot, right
   in front of a Yellow Keycard Door.

   Optionally, you can go through the yellow door and then into a
   control-room area which has the ASSAULT RIFLE. But go back to the
   industrial train depot to obtain a bunch of secret stuff.

   So, retrace your earlier steps to the Security Station which you can now
   access! Take the supplies and interact with a terminal to unlock the doors

   Continue re-tracing your steps. In the hallway, on the floor to the right,
   is a Hatch. Open it and drop down for SECRET 2.2. Find some The Possesseds
   and 2 Imps, along with ELITE GUARD 2.1 and a PLASMA RIFLE (SECRET 2.3). To
   get out of this area, you'll find a Grate that you can kick open.

   This will drop you into the location of the Developed Outdoor area fight,
   which is now vacant, but some Health may have re-appeared.

   Continue retracing your steps by pressing the Call Elevator button on the
   lower level, and find the Field Drone. I recommend using it to get the
   Heat Blast modification for the Plasma Gun.

   Now, instead of going forward, turn right into a door that was unlocked
   when you accessed the Security Station a minute ago. This is SECRET 2.5.
   Follow the blood to a duct, crouch, and go through to get to a steamy room
   you could see into earlier. SECRET 2.7, ELITE GUARD 2.2, and some armor
   and health.

   Exit the door by interacting with it, to the Industrial Train Depot.

   Go through the Yellow Keycard door, and Open the Airlock from the control
   room in this area. Take the Assault Rifle if you didn't get it earlier.

   Enter the Airlock, then Cycle it to access the red outdoors.

Mission 2: Fight 2.7: Outdoor Fight

   This sprawling fight occurs mostly in the lower level of a two-level area.
   It's mostly Possessed Soldiers and Imps- lot's of them. I recommend
   running through using Heat Blast (watch out for explosive barrels), and
   using the Chainsaw on the Possessed Security. Then grab the Berserk
   Powerup to kill the majority of the remainder.

Mission 2: Accessing the Secret after the Outdoor Fight

   Follow the uphill path from the entrance to the second floor. Right as you
   get onto the second floor, look for a bloody crate.

   Jump onto the crate, then jump up and forward onto a duct. Turn right and
   go shortly up along the top of the duct. Turn around and jump onto a
   higher, shinier duct.

   Walk along it, with breathtaking martian views, keeping an eye out for a
   yellow landing to the right of the duct.

   Jump onto the landing - and jump again to a rooftop.

   Walk on the roof to an alcove in the building (turn left and go over a
   pipe, then turn right into a duct), to find SECRET 2.6, COLLECTIBLE 2.1:
   "Doom Marine Model, Doomguy".

   Go back - and on the rooftop look left for a hatch that you can use to
   drop down into the control room with the in-game waypoint.

Mission 2: Realigning the Communication Satellites

   There's a corpse whose handprint will grant you access to begin the
   realignment process. Interact to achieve this morbid security victory.

   Follow waypoints, to go down the elevator down to the next tiny fight.

Mission 2: Mini Fight 2.8: Imps after Aligning the Bridge

   3 Imps climb up; one more on bridge.

Mission 2: Crossing the bridge

   Jump across where the surprising Imp jumped up. Turn right and jump where
   a green light strip can be seen.

   There are symettric platform to the left (away from the base) and right
   (toward where you came from). Jump to the right.

   Take the platform back toward the building: there should be a suit of
   armor in front of you.

   An automatic door will open, with 2 Possessed Soldiers and 1 Possessed
   Security. Toss a grenade back in. The chainsaw can be a good way to deal
   with the Shielded guy.

   CHECKPOINT.

Mission 2: Mini Fight 2.9: VEGA Terminal Entrance

   1 Possessed Security and 2 Possessed Soldiers. (Use a grenade or Heat
   Blast or a chainsaw.)

Mission 2: Fight 2.10: Entranceway / Control Room Area

   Three Imps and a few The Possesseds. In the entrance hallway, there's a
   door to the right that leads to a Munitions Crate.

   There's a assault rifle and CODEX ENTRY "Monsters / Possessed Security"
   here.

   In the control console area is a screen you can use to open the next door.

Mission 2: Fight 2.11: VEGA Hallway

   A Possessed Soldier will run in as soon as the door opens.

   Many The Possesseds, 3 Possessed Soldiers, and one Possessed Security.

   Often the Possessed Security guards a hall to the left. It is worth
   exploring. After climbing, an Imp will spawn in front of you. There is
   ELITE GUARD 2.3 and a Munitions Crate.

Mission 2: VEGA Console area

   This is a semicircular area with a central room.

   But first, climb the crates at left and jump to find SECRET 2.4,
   COLLECTIBLE 2.2, "Heavy Assault Rifle Model, Bronzeguy".

   Enter the central room and watch the cut scene.

   I recommend directing the Argent Energy toward your Health.

                         Mission 3: Foundry "Meltdown"

   This mission has 4 Gore Nests you need to destroy. The first two can be
   destroyed at any time. The third requires a Yellow Keycard and the fourth
   requires a Blue Keycard. Getting the Blue Keycard requires a Yellow
   Keycard.

   Here's a quick description of each Gore Nest:

     * Gore Nest 1: In the area behind the Field Drone
     * Gore Nest 2: In the main area on a damaged platform.
     * Gore Nest 3: Accessed by the Yellow Keycard, in a side-foundry.
     * Gore Nest 4: Accessed by the Blue Keycard, in a locker room area.

   The Main Foundry Area is the large open area with molten metal floors and
   platform-walkways.

   Notes on Combat Challenges:

     * Three Possessed, One Barrel: the easiest opportunity for this is early
       on, but you can also do it in the Argent Cell fight.
     * Curb Stomp: Gore Nest 2 in the yellow molten Main Foundry Area is the
       easiest, but there's a lot of random Possessed Soldiers around.
       (Unlike Mission 9's "Variety Is the Spice of Death II", Hell Razers do
       not count for this challenge)
     * Quite the Collector: easy with this guide, I hope.

Mission 3: Mini Fight 3.1: Small Initial Gang

   From the entrance area, exit into the Main Foundry Area. Jump left over a
   gap in the catwalk.

   The following fight does not spawn every time, especially if you die.

   To the right, across a bridge, is a Possessed Soldier you can
   Death-From-Above Glory Kill (as needed for the combat challenge "Curb
   Stomp") and many possessed you can kill with one barrel (for Combat
   Challenge #1).

Mission 3: Gore Nest 1 (Ante-Room)

   Go back, though, through the door and find FIELD DRONE 3.1. Use it as you
   wish (I tend to like Assault Rifle's Tactical Scope). There is also CODEX
   ENTRY "Environments / Foundry" here.

Mission 3: Gore Nest 1: Mini Fight 3.2: Side-Foundry

   Keep going back past some firey doors to a control console. You can try to
   unlock the door (you don't have access) or watch a replay to see where the
   Yellow Keycard Guard has gone.

   If you turn so we are facing away from the control console, there are two
   passages: the entrance on the right, and the left passage has the keycard.

   If you enter that passage, you'll see that the catwalk has broken, and you
   should barely be able to see a deceased guard on the other side, leaning
   against a non-functional door: he has your Keycard.

   If you try to jump across, you'll land on a platform below. To your right
   is a small room with ELITE GUARD 3.1.

   Follow the green lights to jump around and get up to a platform at the
   same height as you started. The highest platform should say MIXOM. Look up
   and right to see a square opening you can jump into: this is SECRET 3.1,
   there is a suit of armor here.

   Finally, jump to the platform you could see from across the gap. Interact
   with the corpse to grab his biometric ID (ie his arm). Turn around: you
   can jump the gap easily in this direction - but watch out for an Imp that
   appears. The flaming door ahead is where the Gore's Nest is located.

   Go to the control console (veering left) and use the dude's arm. Turn left
   twice to find the Gore's Nest.

Mission 3: Fight 3.3: Gore Nest 1

   This fight takes place in a somewhat dim and dirty one-story area. But,
   it's just ~5 Imps and ~3 Hell Razers so it is fairly quick.

Mission 3: Gore Nest 2

   This gore nest is the only one in the Foundry's Main Area.

Mission 3: Fight: Gore Nest 2

   Pre-Fight: A good place to use the heat blast, and a fine place to work on
   the Curb Stomp combat challenge. This is a mix of The Possessed, Possessed
   Soldiers, Imps.

   Gather supplies then destroy the Gore Nest.

   As suggested by the Gas tank near the Nest, you may wish to use chainsaw
   here since you might be low on ammo. Otherwise, just use a mix of weapons;
   I often mostly use Heat Blast here. This is a mix of Possessed Soldiers,
   Imps, and Hell Razers.

Mission 3: Fight: The Tunnels Above Gore Nest 2

   This system of tunnels can be entered any time, except during combat. But
   you'll probably want to do it right after Gore Nest 2.

   It connects various stories of the Main Foundary Area overlooking Gore
   Nest 2.

   This is more of an exploratory area than a fight, but it is strewn with
   minor demons.

   It is hard to describe all the turns and the 3 entrances to this area, but
   it can be explored easily enough. Just make sure you find:

     * CODEX ENTRY "Monsters / Imp" in a dead-end room with some armor
     * SECRET 3.4: To get to this secret area, you'll have to jump up to a
       nondescript ledge. Look for a room with a rotating-red ceiling-mounted
       light, over which is painted "UAC-HAL". Looking at that, the ledge is
       slightly higher and to the right of it. Enter into it, and it'll twist
       around to get to the secret and the ROCKET LAUNCHER.

   There are three access points, all overlooking Gore Nest #2. Here's a
   description of each of them:

     * Lower Entrance / Gore Nest #2 Access
          * From the vicinity of Gore Nest #2: looking out to the main area,
            the catwalks on the right should have two stories. Get to the
            upper story, and you'll find a small doorway.
          * From the tunnel, look for blood streams and an obvious exit.
     * Middle Entrance
          * From the tunnel: look for an observation room; the door it
            outside the window looking in.
     * Upper Entrance / Yellow Keycard Guy Access
          * From the guy: go out to a downward staircase; at its bottom turn
            into a small door.
          * From Tunnel: look for a green-lit room with 2 large white boxes.
            Stand on the box(es) and jump to a yellow patterned ledge.

Mission 3: Fight: Obtaining the Yellow Keycard

   To get here, go out of the Field Drone area, and go straight veering
   around the Blue Keycard Area. Before you enter, you may see some Plasma
   Ammo.

   4 Imps, a Possessed Security and two Possessed Soldiers in back are ready
   to fight you. The Shielded guy is the biggest problem, and the chainsaw
   may be the most effective way to deal with him.

   Taking the Keycard creates a CHECKPOINT.

Mission 3: Fight: Getting Away with the Yellow Keycard

   Exiting the area triggers the creation of 2 Imps, a Hell Knight, and (down
   the hall) 2 Possessed Securities. I usually run to the Field Drone
   location, lobbing a grenade behind me. The Hell Knight is the only big
   problem - in fact, often the other attackers will fight themselves to
   nothing if you merely wait.

Mission 3: Fight: Argent Cell

   In order to use the Yellow Keycard, you'll have to find a mishmash of
   demons in a hot foundry area. The barrels provide an easy way to kill them
   en masse.

   ARGENT CELL 3.1 is found in the corner, in front of a defunct door.

   SECRET 3.3 is the classic doom level. From the yellow keycard area, look
   back on the walkway you came in on. There should be a box/crate on its
   right side. On the side of that is a Lever, which will open a door in the
   fight area that enters CLASSIC MAP 3.1 "Doom - Nuclear Plant".

Mission 3: Using the Yellow Keycard

   As you approach the yellow keycard door, a Hell Knight will surprise you.
   Entering the door creates a CHECKPOINT, so it is advisable to stock up on
   ammo, armor and health before entering.

Mission 3: Fight: Hall after Yellow Keycard, before Gore Nest 3

   After picking up whatever supplies from the anteroom, including CODEX
   ENTRY, "UAC Personnel / Samuel Hayden", enter a hall where some repair
   robots appear to be working on a crate.

   Initially there are just two Possessed Soldiers (on the left-hand side) If
   you stay near the entrance wall, nobody else will spawn, and it is
   suggested to kill these guys before charging in.

   Then, a Hell Knight, a (few?) Imps, an a few Hell Razers will spawn.
   Lobbing a grenade at the barrel can help, but the Hell Knight has to be
   dealt with.

   SECRET 3.5, COLLECTIBLE 3.1, "Plasma Rifle Model, Prototypeguy" can be
   found in a crate being robotically worked on (climb on top of it then
   inside).

   SECRET 3.2, ELITE GUARD 3.2, can be found by climbing crates at the back
   of the room. There should be a chainsaw resting against the crates
   (initially).

Mission 3: Fight: Gore Nest 3

   A Possessed Soldier and Possessed Engineer constitute the pre-fight for
   this Gore Nest.

   Destroy the Gore Nest.

   A few Imps and a few Hell Razers will spawn, and the finale is a Hell
   Knight.

Mission 3: Finding the Blue Keycard

   The map should probably show the Auto-Map - it's on the catwalk area.

   Exit through the upper down in this area and you'll immediately run into
   the Blue Keycard holder (a corpse). Take the keycard.

   At this point, 2 Hell Knights will spawn far away. First is back at the
   door you opened with the yellow keycard. He is quiet and may surprise you.
   The second Hell Knight spawns near the field drone at the beginning of the
   level. (These will not respawn if you die.)

   Drop down to the area where you "found" the Yellow Keycard. This is a good
   time to get SECRET 3.6, COLLECTIBLE 3.2, "Possessed Engineer Model,
   Vaultguy". Look for the 3 streams of molten metal. Get onto the walkway in
   front of them, and look straight down to see a little landing just inches
   above the molten metal. Jump onto this platform and look for the doll.

Mission 3: Fight: Gore Nest 4

   There's no pre-fight: destroy the Gore Nest.

   This two level area has a sheltered locker room on the lower floor, where
   one Imp will spawn immediately but most of the demons (Imps and Possessed
   Soldiers) spawn upstairs. Lob grenades or charge in - eventually they'll
   come down the stairs, but slowly.

   It ends with a Hell Knight - since there's Gas, a chainsaw is a good
   approach.

   The upper story has a Health Station.

Mission 3: Once all four Gore Nests are destroyed

   You may be ambushed by some Imps as you find your way to the waypoint.

   The Turbine Room door, which the game will guide you to, is now unlocked.

   CHECKPOINT.

Mission 3: Fight: Turbine Room

   This fight has two waves, both start with a lot of Imps and Hell Razers.
   At the end of the first wave is 1 Hell Knight; the second wave ends with 2
   Hell Knights. The waves are separated by a little earthquake.

   After completing the fight, exit at the top of the room, on the opposite
   side as the entrance.

Mission 3: End of Mission

   You come into a hall with ELITE GUARD 3.3 propped up on the left side.

   Open the Shutters (interact with the screen), to watch a cut-scene with
   Olivia Pierce.

   Immediately after that, an Imp and 2 The Possesseds will spawn. (You could
   get one more Heat Blast multikill here)

               Mission 4: Argent Facility "Beginning of the End"

   This area will be revisited in Mission 6: Argent Facility (Destroyed),
   which mostly shares the outdoor areas, but the indoor areas are completely
   separate.

   Notes on Combat Challenges:

     * Walk the Path and Bird's Eye View: easy with this walkthrough,
       hopefully.
     * To Be Knighted: glory kills from above on these guys is pretty hard
       since they are so tall: unless you are replaying this with the jump
       boots, you'll have to jump from higher ground to do this. The Dazed
       and Confused rune can be useful to give you more time to figure out
       how to jump over them - it usually requires jumping from above, unless
       they are crouched. Of course, a cheesy way is to replay this mission
       after you have the Jump Boots which make it substatially easier.
     * Bird's Eye View: See Secret 4.1 below

Mission 4: Introduction

   Go forward and Open the Airlock to find yourself in an industrial open-air
   area: immediately in front of you is a trash fire and ahead of you is a
   blocked-off bridge.

   Look left. There should be a octagonal structure with 2 Platforms, a Lower
   one and an Upper one. Jump to the Lower Platform. Now, look left for some
   green marker lights on the cliff-like rocks. Jump up a few of them (follow
   the green marker lights), and on to the Upper Platform.

   Now, look for an broken bridge - jump there and cross another small
   bridge, to your first Rune Challenge, RUNE CHALLENGE 4.1: "Vacuum". This
   challenge is not too bad, and the rewards are quite good, so you should do
   it. Time is really of the essence on this challenge.

   After succeeding at the Rune Challenge, the Rune is NOT automatically
   equipped, so go to the Rune section of your Dossier and select the Vacuum
   Rune.

   If you want, grab the ammo on the right pathway, but the mission continues
   to the left.

   In front of a closed door, you'll see some Health and Ammo, and CODEX
   ENTRY "Environments / Argent Facility". Less obviously, behind some
   barrels to the left, is a Classic Doom Level Lever - the lever is in the
   dark and hard to see. Pull it: the "retro" level itself will be easy to
   see ahead.

Mission 4: Fight: Gore Hallway

   Enter the automated door to a hallway that has been thoroughly decorated
   with entrails. Midway down this hall, to your right, is (assuming you
   pulled the lever above) the SECRET 4.5, CLASSIC MAP 4.1 "Doom - Toxin
   Refinery".

   Continue out the hall to run into 2 Possessed Securities and a bunch of
   The Possesseds. Some Imps will spawn soon; once you kill them you'll get
   more Imps and a Hell Knight.

   You can retreat into Hall (and it can be a good way to start the fight,
   say, with a few Grenades). But the new monsters will start to spawn behind
   you, and it may be easier just to stay in the open.

   CHECKPOINT.

Mission 4: Fight: Force-Field Gore Nest #1

   Jump over a crude but wide blockade to get to a view of a big glowing
   rectangular blue force-field. The gore nest is just behind it.

   Looking down, you may see some Imps fighting - they will see you soon
   enough. Kill these few Imps, along with the Possessed Engineers and The
   Possesseds stumbling around.

   Destroy the Gore Nest.

   You'll have to deal with 2 Hell Knights, 2 Hell Razers, and a bunch of
   Imps.

   CHECKPOINT.

   It's probably worth going back to the Blockade you entered from, and look
   around for a cave (it'll be on the left as you walk toward the Force
   Field). The cave has ELITE GUARD 4.1. There's some ammo (etc) here.

Mission 4: Fight: Argent Cell

   (It might seem logical to destroy the Argent Filter associated with the
   Gore Nest first, but due to how the Checkpoints work, I suggest doing
   things in this order)

   You can now go and destroy the Argent Filter, but I think it makes sense
   to first deal with the Argent Cell.

   The Argent Cell is in the building on the left side of the force-field
   when looking at it - on the opposite side of the gore nest from where you
   entered. There should be some Health in front of it.

   Entering, there will above 5 Imps spawned gradually.

   Once they are gone, CHECKPOINT.

   Now, find ARGENT CELL 4.1 behind some tanks. Use it: most players will opt
   for Health.

Mission 4: Argent Filter associated with Gore Nest #1

   Open the small door on the lower floor near the Gore Nest's old location.
   Enter to find a Possessed Engineer and a few The Possesseds. There is also
   CODEX ENTRY "Personnel / VEGA". Make a left to follow the waypoint and
   interact with the Argent Filter for a cut scene.

Mission 4: Under the Force Field (Optional)

   There's a small treasure area directly below the big blue force field.
   Face it, and go left down a path (which has a Munitions Crate). Turn right
   and descend 3 floating Islands of rock to get to a partially open bay door
   (visible from above).

   Inside you'll find Gas, shotgun and plasma ammo, and a little armor. But
   most importantly FIELD DRONE 4.1.

Mission 4: Fight: Tank Gore Nest #2

   Near the entrance for the Argent Cell building, find two stacked crates,
   and a suspended one: these can be climbed, and from the top of the
   suspended crate, you can jump to the second floor of this building.

   This battlefield is distinguished by a recognizable and large Union
   Aerospace tank (which you can jump on).

   Pre-Fight: 3 Imps run down from above very quickly, be prepared to take
   care of them.

   Fight: Imps and Hell Razers with 2 Hell Knights.

Mission 4: Argent Filter associated with Gore Nest #2

   Go into the closest door to Gore Nest 2, on its same level - it is
   somewhat inset - a waypoint should be leading in this general direction.
   Inside the building, go along the walkway to a closed green door with the
   waypoint behind it by 15 meters. Enter and interact to destroy the Argent
   Filter #2 and get a CHECKPOINT.

   There is also a Plasma Rifle here.

Mission 4: Rune and Secret

   From the small room containing the Argent Filter, turn right to a large
   floor with large lifts. You can probably see the glowing green RUNE
   CHALLENGE 4.2: "Dazed and Confused" on the lift in the opposite corner of
   the building (from the entrance, look at the opposite corner - the rune is
   on the structure just to the right of center).

   Once done with the rune, look for a large hole that is serviced by a lift
   (now down). Jump down there, and into a hallway. On the left you should
   see a small block on a larger block, making a natural stairway. (A drone
   delivers it- wait a few seconds if the blocks aren't climbable - or you
   might have to go back to the argent filter you destroyed to trigger it)
   Climb up, and turn right to see a service walkway which you can jump onto
   to find SECRET 4.2, COLLECTIBLE 4.1, "Hell Knight Model, UACguy".

Mission 4: Back Access Walkway (Secrets, Optional)

   This lonely walkway is the only dirt path descending from Gore Nest #2 /
   Union Aerospace Tank. It provides alternate accesses to a Lab and the icy
   Gore Nest #3; these are described below. It has a broken bridge midway.

   If you face the Union Aerospace text on the large tank, go down the dirt
   walkway to its left. It is the only dirt walkway descending from this area
   - it'll turn to a metal grated walkway - then there's a gap you must jump.

   Before the metal grated walkway, look to your right for a misty cargo
   alcove with a lone crate. Jump on it to get to the second level.

   You should find a Munitions Crate here.

   A single Imp will pop out if you follow the walkway to its end.

   If you stand on the platform at the edge of building, you should see a
   rectangular duct that runs along the outside of the structure. Walk on it
   for a bit until you get to the next alcove: enter to find SECRET 4.3,
   COLLECTIBLE 4.2, "Rocket Launcher Model, Stealthguy".

   Go back to the first alcove, but jump across to a green-lit cliff; jump
   again to a walkway and kill a few demons (a Possessed Engineer and a few
   Possesseds). (This is helpful to get the maximum combat rating)

   Finally, go to the end of the walkway (it becomes a catwalk) to a door
   (entrance to the Icy Area). Watch out for the Imp! At the end, go left
   onto a natural walkway. This is SECRET 4.4. There's a Possessed Engineer
   and a few Possesseds, but most importantly, the SUPER SHOTGUN.

Mission 4: Lower Area with Elite Guard #3

   Start at the Force Field (Gore Nest #1) - when facing the field, go down
   the path to the left.

   You should see an active door, and a series of plateaus that lead to a
   Munitions Crate. Immediately to the right of that is a level path that
   becomes a sidewalk for a building. Some Possesseds appear here. At the end
   of the walkway is ELITE GUARD 4.3.

Mission 4: Fight: Lab (Optional)

   This area has a Health Station, FIELD DRONE 4.2, Gas, and CODEX ENTRY
   "Monsters / Hell Razer", but isn't necessary to the completion of the
   Mission.

   Field Drone #2 is on the upper level - it can sometimes take a few seconds
   to fly in once combat is over.

   It has two entrances:

     * Normal: From the site of Gore Nest #2 / the Union Aerospace Tank,
       climb a crate to a balcony. The door enters the middle story of the
       Lab.
     * Sneaky: From the site of Gore Nest #2, walk down a dirt path to an
       enclosure with some blocks on your right. If you look up, you should
       see a greenlit ledge to your left, which is your goal. Climb onto the
       blocks, at right, then onto a grating looking onto the greenlit cliff.
       Jump across and open the door to be in the lower story of the Lab.

   The Possessed Guards tend to be in the lower story and entering there
   catches them more unawares, maybe.

   There are also 5? Imps and a bunch of Possesseds and Possessed Engineers.

   You'll get a CHECKPOINT when the bad guys are cleared.

Mission 4: Fight: Icy Gore Nest #3

   There are 3 entrances to this area:

     * Lower Entrance: from Gore Nest 2 (the Union Aerospace tank), go down a
       dirt path to where it becomes a catwalk instead, to the end at a
       active motion-sensing door.
     * Mid-Lower Entrance: This is probably the "main entrance". From the
       blue force field, go on the path on its left side to a building
       labelled in large letters "COOLING TOWER".
     * Upper Entrance: Access from the long curved exterior walkway with
       Elite Guard #2.

   It matters little.

   Prefight: you'll have to deal with 5? Imps and 2? Possessed Soldiers and a
   bunch of The Possesseds.

   SECRET 4.1: You can actually use this area at any time.
   It is the through the door on the lowest floor area. There's the Auto-Map
   in here, and it'll CHECKPOINT. Of course, the Auto-Map achieves the
   "Bird's Eye View" Combat Challenge.

   Fight: Once the Gore's Nest is destroyed, 1 Hell Knight spawns immediately
   along with a wave of Hell Razers and Imps. There's Gas on the second level
   (and other supplies) in case you want to chainsaw anyone.

   Post-Fight: Now, go in to destroy the Argent Filter.

   There's a Munitions Crate, Gas??, a Health Station, CODEX ENTRY "Monsters
   / Hell Knight". Destroy the Argent Filter and go outside for the last
   battle in this icy area.

Mission 4: Fight: Destroying the Icy Argent Filter

   This is your introduction to the Summoner. She will spawn centrally the
   instant you exit the control booth. The Rocket Launcher (especially with
   Lock-On) is a nice approach, as is the Chainsaw, but she can really be
   killed by any weapon.

   Besides her, there are 3? Imps and a Hell Razer, making this an otherwise
   small fight.

   CHECKPOINT.

   I recommend leaving the building through the top exit, above the Auto-Map.

   You'll be on a walkaround that going alongside the building, a few
   Possesseds and a Hell Razer will surprise you be spawning in front of you.

   At the end of this walkway, find ELITE GUARD 4.2.

Mission 4: After Destroying the 3 Argent Filters

   A new Gore Nest will appear: it's on the upper story and easily visible.
   You have to get to it from the building below, which once housed ARgent
   Filter #2.

   Climb the crates, following the waypoint to the upper-story of the huge
   hangar, right next to Rune #2.

   Exit the door toward the waypoint (approx 80m away), stocking up first if
   necessary and possible. There should be a Munitions Crate ahead, and to
   the left is the exit to the Gore Nest.

Mission 4: Fight: Final Gore Nest

   Pre-Fight: there are 2 Possessed Soldiers, a Hell Razer, and an Imp.

   Destroy the Nest.

   Fight: a Hell Knight and a Summoner are the main act in this fight -
   there's also a few Imps and Hell Razers. However, there's a Berserk
   Powerup, which compensates a lot (in fact, if you have all the Powerups
   for the Praetor Suit, you can probably kill everything with that single
   Berserk Powerup).

Mission 4: Destroy Primary Argent Filter

   Enter the building and face left for ELITE GUARD 4.4.

   Follow the waypoint to another Argent Filter (looks like the others).
   Destroy it, and watch the cut-scene.

   Follow the waypoint and Exit the Facility.

                 Mission 5: Argent Energy Tower "Argent Tower"

   We start the level getting new Jumping abilities, the Jump Boots. Then we
   cross a damaged bridge to the Tower itself.

   The tower is big and tall - most of the level is spent ascending it.

   Notes on Combat Challenges:

     * Chiropractor: Imps are a bit scarce in convenient locations. There are
       a lot on the bridge, but you'll have to be slightly patient to lure
       them into Glory Kill range, and even then sometimes they'll be at the
       back of a platform and it's not possible to get behind them. (Use the
       Dazed and Confused Rune whenever you are attempting this challenge).

   There are a number in the fight outside the tower, including 4 near the
   entrance to the fight (and checkpoint). There are a few in the first big
   fight, and there's 4 scattered at the upper regions of the tower. Finally,
   there's some in the giant fight at the end of the level.

     * Searching High and Low: easy.
     * Overkiller: there are 3 Quad Damage Powerups: in the fight just
       outside the tower, in the fight in the base of the tower, and in the
       truncated big fight at the end of the mission. It is quite possible to
       achieve this in any of those fights: as long as you use the powerup
       you'll probably be fine. I recommend Plasma Gun/Heat Blast for bulk
       killing.

Mission 5: Fight: Intro to Level, and Revenants

   You start on a useless platform, and have to jump left to get to the
   Maintenance Hangar that VEGA alludes to. Upon entering the building, look
   right, and you can see a Revenant eating a corpse. It soon comes down to
   attack you. There are a gaggle of demons on the floor below you, and more
   will spawn when you drop down to the lower level (as you must to get to
   the locker room with the needed boots). In total, there's about 3
   Possessed Soldiers, 3 Hell Razers, 3 Possessed Engineers. (No Imps,
   unfortunately, as it would help with the Chiropracter challenge.)

Mission 5: Maintenance Hanger miscellany

   Enter the locker room and retrieve the Jump Boots, as well as CODEX ENTRY
   "Environments / Argent Energy Tower", various Ammo, and a Health Station.

   Exiting the locker room, go right (back toward the entrance) and
   double-jump up onto a platform; U-turn and look left for another platform
   to up-jump. Then down-jump into an enclosed area with a Rune Challenge
   (which was visible from before through some steamy glass), a suit of
   armor, and Gas can. To exit this area, jump down.

   Jump up the same platforms used to access the RUNE CHALLENGE 5.1 "Ammo
   Boost", but look across the area for a floor you can jump to, under a
   low-beam; some armor is at the end of the jump. To the right is a crate
   and some rockets, but ignore them for now, and go left. There is a
   platform to jump up on, and if you look around, you'll see another
   green-lit platform above to jump on. Looking around from the top platform,
   you should see a pink-lit short alcove that you can drop into: there's
   SECRET 5.1, ARGENT CELL 5.1 here.

   Hints on Rune Challenge, "Ammo Boost". The challenge is to not miss anyone
   - I find that I jump make 1 1/4 laps around the periphery of the area,
   looking into the center to shoot any stragglers.

   Ammo Boost isn't exactly necessary, but it (and its upgrade) make ammo
   much more available - especially BFG ammo, once you have the Upgrade and
   of course the BFG itself.

Mission 5: Crossing the Bridge, and Secret Guardhouse

   Before crossing: make sure you have Argent Cell #1 and Rune Challenge #1.

   The bridge starts with a crate and some Rockets. Use the crates to jump
   left onto the bridge proper. Continue along. You'll jump down to a
   platform.

   At this point, you can expect to be ambushed by ~8 Imps, 2 at a time. They
   are all over this gigantic damaged catwalk bridge, you can kill them,
   ideally by Glory Killing them from behind, to work on achieving the
   Chiropracter Challenge.

   From the tunnels, you can and should access FIELD DRONE 5.1 and a SECRET
   5.2. Get on top of either tunnel, and double-jump across to a platform (it
   has a green light). Jump left up a series of airy platforms to an enclosed
   bluish area with 8 The Possessed stumbling about with a Possessed Engineer
   on the upper deck (near a suit of armor). Right outside (on a bridge) is a
   Possessed Security.

   Across the bridge is a guard house, which is Secret #2. Inside is a Hell
   Knight who will charge at you; and 2 Possessed Soldiers and a Possessed
   Security who will stay in the shed. Take them out to find Field Drone #1,
   some health, CODEX ENTRY "Monsters / Revenant". Continue along a walkway
   to some armor.

   When done, jump down to a long walkway that goes almost the whole length
   of the bridge. There's a long gap torn in the walkway: you'll have to
   double-jump across (which is slightly hard to backtrack).

Mission 5: The Far Side of the Bridge

   After the destroyed section of the bridge, look down and right to see
   ELITE GUARD 5.1 (SECRET 5.3) propped up against a wall. Jump down. Getting
   back up is slightly more difficult: jump across the gap to jump nearly
   vertically up a few ledges, looking for yellow ledges; you'll have to
   shimmy left at some point.

   Note: You can get back, but it's not necessary and more difficult than
   jumping forward.

   Cut scene.

   Enter the next room to find a Health Station, CODEX ENTRY "Monsters /
   Summoner", and an AUTO-MAP.

Mission 5: Fight: Tower Exterior

   Enter the next area to surprise 2 Imps. Looking at the Imps, there's some
   Plasma ammo to your left. Ahead, the platform has an upper outer story and
   a lower inner story. Further ahead, on a higher platform, is a Quad
   Powerup - it glows purple brightly.

   It's fairly easy to get a Neck Glory Kill on an Imp, then grab the Quad
   Powerup and use Plasma Gun / Heat Blast to kill basically everything.

   The monsters who are here or will spawn are many Imps and Hell Razers, and
   2 Summoners.

   Leave this area through a Maintenance door on the far end.

Mission 5: Lower Railway (Description and Secret)

   As you can probably see by the Map (in the Dossier), you are at the
   outside of the tall circular Argent Energy Tower. Unmanned trains run
   around it's exterior, and you'll encounter them a few times.

   You should see such an unmanned train going right every 5 seconds or so.
   Use the Munitions Crate, then follow the next convenient train, and drop
   into an unused track. Keep going, and you should see an entrance to a
   human-sized passageway on your left.

   Upon entering the passageway, look back to find ELITE GUARD 5.2. Continue
   to find a Health Station and Codex Page "Database / Argent Energy".

   At some point, the passage becomes narrower and darker, and we can make a
   detour to get the Collectible doll.

   To get SECRET 5.4, COLLECTIBLE 5.1: "UAC Pistol Model / Orangeguy",
   re-enter the unused Train corridor at this point (by veering right).
   Continuing down the corridor, you'll arrive at an unused, stationary train
   car. Get onto it, by double-jumping onto the ledge to your right, then
   double-jumping onto the train car (don't worry: the upper-train won't hit
   you). You should be able to see another dimly-lit ledge near where the
   upper train cars keep entering. I found this jump to be quite tricky. but
   the trick is that you must be facing at the ledge (ie facing perpendicular
   to it / straight at it), which mean you must jump almost sideways, which
   in turn makes dodging the train above more difficult. Once you are on this
   ledge, turn left and go up (parallel to train), then turn around and jump
   into the hole that the upper train is entering. You must keep moving, but
   when you run out of floor, drop to the left, and you'll find the Model.
   Drop down the train area to get back to the Elite Guard, and continue back
   to where the passage narrows and becomes darker.

   OK, continue down this short dingy corridor, and you'll find a Hatch, at
   left, along with some a rocket launcher.

   POINT OF NO RETURN: Dropping down this hatch is irreversible, and a
   CHECKPOINT is created immediately on hitting the ground.

Mission 5: Fight: Base of Tower

   This fight begins with a cut-scene introducing us (somewhat) to the
   MANCUBUS.

   Use the Rocket Launcher or Gauss Cannon (etc) to damage this guy before
   running around for a while taking pot-shots at various demons.

   Once you damage a lot of demons, look for the Yellow Lift that jams you
   into a Qad Powerup. Use Plasma Rifle's Heat Blast to kill a lot of demons.

   Post-Fight: pick up all the Gas and Ammo.

   Midway up there's a tricky little secret. You'll find it after where the
   central red beam (of Argent Energy) is surrounded by rotating and
   stridulating metal shields.

   Continue up, across a long jump to where the red beam is protected by
   shutters that periodically open and close. Look on the map. You should see
   two symmetric arms going up. But one of them has a walkway underneath.
   This is SECRET 5.5, COLLECTIBLE 5.2 with "Summoner Model, Purpleguy". With
   the In-Flight Mobility Rune, this is a piece of cake, but you don't have
   that yet, so you'll have to use one of two approaches.

     * You can actually jump on the gray tubes that run to the platform, then
       jump again onto the platform.
     * Drop from a platform above, and jump in mid-air onto the duct.

   Resume climbing: there's a rotating train that repetitively inserts ducts
   into the central beam. Between when it opens and when it extends the duct,
   you can jump up.

Mission 5: Fight: Midway

   A fight involving Possessed Soldiers, Imps, Revenants and a Hell Knight
   breaks out here. There's a somewhat tricky-to-get-to Invulnerability
   Powerup that can help. It can found be looking for the two protected doors
   a few stories up from the ground level. One is your waypoint (it has a
   suit of armor in front) and the over has the green Invulnerability
   Powerup. Use the blue lifts to get onto this high area.

   After the lockdown is disengaged, continue up to where the waypoint is.

Mission 5: Activating the Drones

   Use ARGENT CELL 5.2 and the Health Station if needed, and interact with
   the screen (at waypoint): "Activate Drones".

   This will cause two pairs of cars (drones) to transport stuff vertically
   from this area to a platform above: we'll catch a lift.

   Exit the control room and find that there's one pair of drones right in
   front of you.

   Instead, go around to the opposite side of the column where the second
   pair of drones is (this is also where the Invulnerability Powerup is).
   (These drones are illuminated in blue; the drones near the control room
   are green) Jump onto a drone and go up: you'll see a platform at the top,
   with (if you look carefully) a lever. Jump to it and actuate the Lever.
   Hitch a ride down with the drone. At the bottom, the drone will plug into
   a socket; when it disengages, you'll see SECRET 5.7, the CLASSIC MAP 5.1
   "Doom - Halls of the Damned" in the back of the socket.

   After that, take any drone up to the top and jump up to the highest
   platform you can. You'll see another rotating plug train. When it stops
   you should be able to jump straight onto it. When it stops again, follow
   the plug and some on to a platform on either side.

   From this narrow inner circular walkway, you'll see 4 arms ascending to
   the outer side of the tower. One of them has a couple of platforms by its
   end: you'll have to take that one, and jump up a few platforms.

   Keep going up, steering clear of the argent beams and taking out 4 Imps.
   Eventually you can hitch a ride up on one of the argent transfer things.
   From the top, the waypoint is right there: a greenlit door to force open.

Mission 5: Fight: Upper Office

   2 Possessed Solders and a bunch of The Possessed await you inside.

   From the office, take the stairs to a Possessed Security, a Hell Knight,
   and a few more minor demons. The passage comes to a dead end.

Mission 5: Ascending to the Top

   From the dead end, you can jump across the tracks through a "window". To
   your left will be Rune Challenge #2, "Equipment Power".

   "Equipment Power" is a pretty easy and fun challenge. Simply use yourself
   as bait to lure the Unwilling into barrels that you shoot. Watch out for
   Unwilling that spawn behind you though!

   After the Rune Challenge, look back across where you jumped the tracks,
   and notice a higher platform you can jump to.

   You come to a pair of elevator shafts. The first one (on the left) has a
   Munitions Crate in plain view. The second one has a Mega-Health down in
   the shaft. Drop down to get it, and retrace your steps.

   From the Munitions Crate, jump onto an obvious ledge system to another
   hallway.

   Before going on, look at the twin elevator shafts. Between them, in the
   hall is a wide brown pillar with orange lettering on it ("UAC E-1" on one
   side, "U-A 46.2" on the other). There's a landing in back between the two
   elevators: ELITE GUARD 5.3 is here.

   Continue up the stairs and through the door to another elevator shaft on
   left, and audio of Olivia.

   Carefully peer down the elevator shaft - you'll see an opening about 6
   lights down: jump and hold forward to land in it - this is SECRET 5.6.
   Here we acquire the GAUSS CANNON, the most powerful "standard" weapon.
   "Open the Turbine" by interacting with the screen, which will open a exit
   from the shaft.

   Take it, and retrace your steps all the way back up to the top of the
   shaft. Note there's a Hologram (sometimes known as a Decoy) and a Plasma
   Gun here.

   Now, jump up to the landing at the far side of the shaft and look at the
   shaft ceiling to see 4 red glowing things - each with a waypoint on it.

   Shoot them to cause a car to fall exposing another higher landing you can
   jump to.

Mission 5: Pseudo-Fight: Before the Countdown Ends

   You could conceivably use this to do some Weapon Upgrade Challenges or
   Rune Challenges, but I usually focus on trying to conserve my 200/200
   which means perservering for a long time, then taking the Invulnerability
   Powerup at some point.

   Another use is to earn Combat Challenge progress. If you killed everything
   else, you should already have the highest Combat rating, but you can get
   just about a full circle if you fight very aggressively here.

   TODO: Timings

                  Mission 6: Kadingir Sanctum "Into the Fire"

   Notes on Combat Challenges:

     * Dead Man Stalking: these guys can be easy to miss.
     * Momentum Swing: fairly easy if you use all the powerups (just don't
       "save" them for too long).
     * Sweep the Leg: there's not a huge number of these guys in convenient
       locations, and the glory kill is a bit hard to execute anyways. Don't
       miss any opportunities!

Mission 6: Fight: To get the Yellow Skull

   Because there are no Checkpoints, this sequence of fights is gathered
   together.

   First, drop down to a plateau with a toxic pond and 3 The Possesseds -
   target-practice. There's some armor. Jumping across to Plasma Ammo, maybe
   a Gauss Cannon.

   Climb up the stairs and kill 3 The Possesseds.

   This is one opportunity to get SECRET 6.4: after killing The Possesseds,
   look up and to your left for a rock ledge you can jump onto, then a
   sequence of 2 more ledges to get a suit of Armor.

   Venturing out will begin the pre-fight; the main fight won't begin until
   you get near the left edge.

   Look down to the next lower platform and you'll see an Imp spawn: you can
   kill it immediately with a grenade. Then a Revenant spawns: I usually use
   the rocket launcher, but whatever works.

   Stand on ledge that has a suit of armor on it. Look down below into the
   Main Pit Area, and soon you'll see 2 Mancubi lumbering around that you can
   carefully attack with the Rocket Launcher (preferably with Lock-On
   modification).

   Quickly jump down the Pit area, to trigger two waves:

     * a bunch of Imps and a Hell Razer, ending with a Hell Knight
     * a bunch of Imps and a few Hell Razers, ending with 2 Hell Knights

Mission 6: Accessing and Using the Yellow Skull

   The game's waypoint will lead you to a switch (only accessible once all
   the above demons are killed). After actuating the switch, walk across the
   pit to a newly opened area with armor and the Yellow Skull.

   Now, find the Yellow Skull Door, by walking up the path from where the
   last fight started. Open the Door to walk in and find CODEX ENTRY
   "Artifacts / Slayer's Testament #1" and ELITE GUARD 6.1.

   Proceed onward to the next fight.

Mission 6: Fight: 2 Summomer Fight

   This fight starts on a plateau overlooking another pit area with T-shaped
   bridges running atop it.

   If you enter but don't move, there are 3 The Possessed you can kill. Once
   you walk out toward the middle of the level, 3 Imps spawn.

   Once you get to the edge of the plateau is when the bulk of the demons
   spawn. On the center of the bridge, a Summoner will spawn. Lock-On Rocket
   Launcher is a good way to get her (as suggested by the Weapon Upgrade
   challenge). Another Summoner spawns on the left side of the lower area.

   2 Hell Knights soon spawn, along with a mess of Hell Razers (etc).

Mission 6: Getting the Blue Skull

   Follow the game's marker to a Chainsaw and Shotgun Ammo. Continue down a
   passage to watch a series of islands appear, in the large cavern where the
   first fight began.

   You can jump directly to the nearest island, or jump down and make
   slightly easier jumps up the islands. (If you want armor, this is your
   second chance to get SECRET 6.4: you can see the suit of armor from above:
   climb the stairs and use some ledges to jump to it) In either event, a
   Skull-Switch is at the top of the islands; pressing it, you'll see a gate
   lift on the lower level. Jump down there, killing The Possesseds flailing
   around.

   The green mist will teleport you to the next area; before doing that, head
   right to pick up supplies and SECRET 6.1, COLLECTIBLE 6.1: "Revenant
   Model, Astroguy".

   Head through the teleporter.

   You'll find a Blue Skull. Upon taking it, a gate will open leading you
   back to the overlook of the Main Pit Area.

Mission 6: Fight: Main Pit Area, part 2

   Before you can do anything, 4 Imps will spawn up here.

   Imps should start spawning below: carefully take them out with grenades or
   whatever.

   A few Cacodaemons will spawn. Two blasts with the Lock-On Rocket Launcher
   will kill them, or you can target their eye with the Assault Rifle, or
   Gauss Cannon works. You'll also need to keep lobbing grenades to kill the
   Imps that like to hang out in the area to the right of the base of the
   long stairs.

   At some point, to trigger more demons, you'll have to descend to the
   floor. Take the Quad Powerup as needed (if you have 2 Power Upgrades,
   you'll refresh your health at this point, so it can be best to wait until
   you are damaged. There is a wave of Revenants and a Hell Knight, another
   Cacodaemon, more Revenants, a Mancubus, and a number of Imps.

Mission 6: Rune Challenge and Using the Blue Skull

   POINT OF NO RETURN: This Rune Challenge is only accessible for a short
   while. The protective gates around it are closed before you get the Blue
   Skull, and after you pass through a holographic ritual taking place in a
   corridor. (XXX: is the Rune accessible during the above Fight??)

   Accessing RUNE CHALLENGE 6.1 requires jumping onto the central Rock that
   held the Quad Powerup. Jump onto the smaller upper island (there are two:
   jump toward the one closer to the Blue Door?). Then you should see a
   man-made (or demon-made) ledge to your right, with a few small Healths.
   Jump, and turn around and look up to see a higher island. Jump to it -
   then continue the same direction to an upper ledge. Climb a short ledge to
   a tunnel leading left to the Savagery Rune Challenge.

   After finishing it, go back to the main rock (where the Quad Powerup was),
   and jump to the "balcony" with the Blue Skull Door. Interact, and you'll
   be in a pale green stone hallway: immediately on your right is an alcove
   containing Gas and a ARGENT CELL 6.1. Further down, is rockets.

Mission 6: Fight: Misc Small Fights in the Cliff Area

   First up, is 4 Unwilling (good Weapon Upgrade fodder for Super Shotgun or
   Heat Blast) with a Mancubus, and a second Mancubus that jumps up when the
   first dies.

   Now is not a bad time to use the Invulnerability which is on a lower level
   near where you exit the tunnel.

   Walking along the ledge, some Imps, 2 Lost Souls, a Revenant spawn. (Kill
   them while Invulnerable to work on the Momentum Swing challenge) (Another
   good strategy here is to retreat and pick them off with the Assault Rifle.
   Often they'll kill each other)

   Island-Jump across to be surprised by 3 Lost Souls, and a Hell Razer (if
   you haven't completed the Sweep the Leg challenge yet).

   Walk through the tunnel behind the Hell Razer, and you'll be on a new
   cliff, with a fire and ELITE GUARD 6.2. First, look left and down and
   you'll see the first Cacodaemon. There is second one, probably behind that
   rocky pinnacle. Lock-On Rocket Launcher is a fool-proof way to deal with
   these guys.

   (Do not forget to visit the Elite Guard)

   Detour for SECRET 6.2: Jump to the Island with the Armor and jump across
   to a lower ledge. Turn right, and a Hell Knight will spawn. Behind him (to
   the left) is a small cave with the Chaingun (the cave is the secret).
   Retrace your steps to the spent Elite Guard across the cavern.

   Island-Hop using the upper chain of islands. At the end of this sequence
   of 5? Islands is a Skull Switch: you will see the Iron Gate to the next
   part of the level raise when you actuate it.

   You won't get a CHECKPOINT until everything is cleared (except the Hell
   Knight)- usually that occurs after the pair of Cacodaemons.

Mission 6: Fight: Second Pit

   Enter to find yourself in yet another large arena centered around a "pit"
   with bloody floors. To your left is a balcony from which you can deal with
   a few demons, most notably 2 Lost Souls. There's a lot of Hell Razers,
   Imps, and Revenants, as well as 2 Hell Knights and a Mancubus at the end
   of the fight (the Mancubus only spawns as you approach the waypoint).

   In the pit, there's a tunnel with many small armor and a Haste Powerup.

Mission 6: Rune Challenge: "Seek and Destroy"

   After the fight a tunnel opens to the RUNE CHALLENGE 6.2.

Mission 6: Extracurricular Activities around the second pit

   You can continue up the stairs for the main campaign path, or you can
   return to the levels entrance and look for two small adjacent caves that
   opened up.

   The right-hand cave has a suit of armor and an Automap.

   The left-hand cave has a green teleporter to a treasure room of sorts with
   CODEX ENTRY "Artifacts / Slayer's Testament #2". You could teleport back,
   but instead look for the exit corridor and find another CODEX ENTRY
   "Environments / Kadingir Sanctum" and ELITE GUARD 6.3.

   Finish the detour by following the corridor and using the yellow lift to
   cross the chasm. If you go straight, then left, you should see the stairs
   leading down to Rune Challenge #2 (and a suit of armor).

   Descend the stairs about halfway (above the decorative gate) and look for
   a ledge to the left you can jump onto to find SECRET 6.3, COLLECTIBLE 6.2:
   "Mancubus Model, Redguy".

   Back at the top of the stairs, find a FIELD DRONE 6.1 (now's time to get
   the Gauss Cannon's Siege Mode) and CODEX ENTRY "Artifacts / Doom Marine".

   A few stray small armor mark the top of a steep staircase. Descend it to
   see a holographic replay of Dr Hayden and some guards.

   POINT OF NO RETURN: Once you go through the gate ahead, you will no longer
   to able to get back to the earlier parts of the level.

   Pass through the gate (it'll open for you), into a fight scene.

Mission 6: Fight: Hell Barons in Arena with two Subarenas

   The fight is already underway between the first Hell Baron and a bunch of
   the Possessed and 6? Imps. By far, the Gauss Cannon in Siege Mode is the
   easiest way to deal with the Hell Baron, then deal with the stragglers
   however you want.

   At some point, a Summoner appears. I usually use the Rocket Launcher, but
   Gauss Cannon or even Chainsaw works.

   Another Hell Baron and some Imps arrive.

   After that's all gone 6? Lost Souls spawn. It is good to take shelter in
   the more protected subarena and pick them off with the Assault Rifle or
   Shotgun or whatever.

   Finally, 2 Hell Barons spawn. I use the Quad Powerup and the Super
   Shotgun. If you already used the Quad Powerup, just keep moving and
   dodging their shots (they move fast, though) and use either the Gauss
   Cannon (you need to move fast, so no Siege Mode) or Super Shotgun.

Mission 6: Onward, after a short Secret Detour

   OK, go back to the large main arena from the last fight. There is a big
   cave. Inside the cave (which can be a bit dark) is a lever: an Original
   Doom Level trigger. The location of SECRET 6.6, CLASSIC MAP 6.1 "Doom -
   Slough of Despair" itself is on the lower floor closer to where you
   entered the arena, or simple walk off the ledge between the two subarenas,
   and drop down.

   Or use the map: it looks quite distinct with a visible arrow drawn into
   the map in the Dossier. Once there, the arrow marks the correct switch to
   press (ie the Left switch). It accesses a Mega Health Bonus (although
   crudely rendered, it is just as effective as a modern-looking one).

   Go back to the subarena that once held the Quad Powerup, and now should be
   decorated with a glowing green circular symbol. When you approach the
   door, it will open.

Mission 6: Fight: some small easy fights

   First, there's about 6 Unwilling in this corridor. they are useful for
   Weapon Upgrade Challenges (eg Tactical Scope, Heat Blast, Super Shotgun,
   Pistol). And 2 Lost Souls to watch out for.

   Instead of charging out island-hopping, turn right, and go up some stairs
   to overlook a Mancubus and 2 Revenants fighting. Help them kill each other
   with a suitable weapon (ie Rocket Launch or Gauss Cannon).

   Go ahead and island-hop over to the largest platform which should have
   some shotgun ammo. Turning left, 2 Cacodaemons will appear: kill them
   (using e.g. the rocket launcher). Go to the edge where the Cacodaemons
   appeared, and look across the chasm to see that a few islands connect you
   to another dilapidated staircase across the way. Make your way over. The
   landing hand a few small health, CODEX ENTRY "Monsters / Mancubus" and
   Gas.

   3 Unwilling and a Mancubus guard another tunnel: you should get a
   Checkpoint here.

   Continue up some stairs, to find 4 more Unwilling wandering around some
   armor: good target fodder.

   A CODEX ENTRY "Artifacts / Slayer's Testament #3" is found.

   The last easy fight is about 5 Imps fighting 10 Unwilling. (I like to work
   on the Savagery Rune and the Seek and Destroy Rune for this easy fight).

   Don't miss ELITE GUARD 6.4 here! (to the left from the way you entered)

   Enter a well-stocked tunnel ending with CODEX ENTRY "UAC Personnel /
   Olivia Pierce" for a CHECKPOINT preceding the final fight of the mission.

Mission 6: Fight: Finale

   It comes in unseparated waves:

     * 4? Imps and 3? Hell Razers
     * 2 Hell Knights
     * 4 Revenants
     * 3 Mancubi
     * 2 Hell Barons and 1 Mancubus

   I tend to save the Quad Powerup and for the end; get the Armor on the
   toplevel (a sometimes overlooked location) early on to make it easier.
   Keep on the move and kill quickly.

   Walk up the hill to a holographic replay of some sort of ritual with a
   casket.

   Interact with the screen ??? to exit the level.

             Mission 7: Argent Facility (Destroyed) "Hell on Mars"

   Notes on Combat Challenges:

     * Skeet Shot: Revenants fly into the air periodically to target you, and
       so the challenge isn't so much shooting them as killing them (they can
       take a lot of damage). Gauss Cannon/Siege Mode will reliably kill them
       in one hit; Rocket Launcher/Lock-On will reliably kill them in two
       hits. So these are my favorite weapons for this challenge.
     * Close Encounters: there's a fair amount of gas in this level, but it
       can be easy to forget to use the Chainsaw. Note that it can be best
       just to mostly fulfill the challenge on some easier demons, since they
       take much less fuel.
     * Knowledge is Power: easy

Mission 7: Introduction

   Pick up CODEX ENTRY "Monsters / Barons of Hell"

   Go ahead and exit to the outdoor walkway, turning right (since left is
   blocked by fire).

Mission 7: Fight: One Cacodaemon on Walkway

   Be surprised by a Cacodaemon; it's a bit annoying on this narrow walkway-
   with timing you can get it in one Gauss Siege Cannon, but one have space
   to dodge it as well. (You can actually get the drop on it, if you are
   prepared)

Mission 7: Getting back into Argent Facility

   At the end of the walkway, turn around and look for a walkway to jump up
   to. Next, jump across to a train and follow it to a small landing with two
   tarp-covered crates. Behind these crates is a lever for the Original Doom
   Level. After actuating the lever, drop down to another walkway/landing
   with a grated floor, and turn around to see a large octagonal pillar with
   a large "1" on it. Behind this pillar is SECRET 7.6, "Classic Level / Doom
   2: Underhalls".

   Immediately upon exiting this area, turn right, to see a right-dirt
   floored alcove with some crates. There is SECRET 7.4, COLLECTIBLE 7.1,
   "Cacodaemon Model / Rageguy". There's also some armor and Gas.

   Now, jump your way up to the highest accessible walkway.

   You'll get a CHECKPOINT shortly before a long double-jump. It's not really
   difficult though. Continue until you are looking into a damaged corridor
   which crosses the chasm.

   Drop into the hallway through the gaping hole in its roof. Turn around to
   find an ELITE GUARD 7.1 (along with some armor and shotgun ammo).

   Go forward to the computer area. Find CODEX ENTRY "Environments / Argent
   Facility".

   Interact with the computer for a 48 second cut scene, whose immediate
   consequence is that you need a yellow keycard. A marker will take you to
   the airlock, which has a screen you can interact with.

Mission 7: Fight: Side Cargo Bay Exterior

   While you may not see monsters immediately, they are just to the right: a
   Hell Razer, a Possessed Engineer, and 6? The Possessed. You can take care
   of many by shooting the barrel. Expect 2 more Revenants, Imps, Possessed
   Soldiers, 2 Cacodaemons, and a Hell Knight.

Mission 7: Fight: Maintenance Exterior

   Drop down to another former gore nest location, near the large Union
   Aerospace tank, on a ground area with lots of fire, to get another small
   fight with Imps, Hell Razers and a Hell Knight.

   There is a Hologram device near some ammo.

   Look down into the next area. This is the area that used to have a blue
   Force Field, but now just has some fires. You should see the pale-orange
   glow of a Berserk Powerup. Drop down.

Mission 7: Fight: Main Cargo Bay

   First to appear will be 2 Cacodaemons and 1 Imp. One Cacodaemon often
   starts very low and can be chainsawed to solve several problems at once.

   After that, Imps, 3? Revenants, and a Summoner appear.

   In fact, the Berserk may outlast the fight: you can perhaps even you it to
   kill some stuff in an adjacent area.

Mission 7: Fight: Main Cargo Bay Adjacent: old platform area

   This area is easily skipped.

   There's a Hell Knight and a few Imps.

Mission 7: Fight: Main Cargo Bay Adjacent: through tunnel

   This area is easily skipped.

   A Hell Knight, a Hell Razer and at least 1 Imp.

   This is the area that had the Lever for the classic doom secret in Mission
   4.

Mission 7: Accessing Rune Challenge "In-Flight Mobility"

   From the Old Platform Area, there's a blue lift that'll drop you on the
   rock for this Rune, RUNE CHALLENGE 7.1.

   Or, you can jump across from the cargo crates in front of the Security
   Station Doors.

   NOTE: This challenge is frustrating for many people, since it has little
   margin for error. However, it is worth the practice, because the Rune is
   critical for some of the bosses.

   From this location, you can drop down SECRET 7.2 which has a Mega Health
   and ELITE GUARD 7.2. Equip the In-Flight Mobility Rune (which you just
   got). Go to the edge of the rock with the chasm and go to the edge of the
   rock. Turn around so that so can drop backward off the rock and face into
   it. Walk backward and fell to a cave, jumping forward right as you see it,
   so that you'll land on the Mega Health. The Elite Guard is in the shaft
   behind it. To get back, jump to a rock with a blue booster.

Mission 7: Fight: Security Station

   To get here, from the Main Cargo Bay, look for a pile of 3 crates to climb
   on. The door should have a marker on it (an in-game destination) and there
   should be Gas here.

   Entering, there's even more supplies littered throughout a gory hallway.

   Interact with the door to get a short cut-scene introducing us to the
   Pinky.

   The fight begins with 2 Pinkies and at least 1 Possessed Soldier (and a
   hard-to-count number of The Possessed in the peripheries- most of these
   get killed by other demons!).

   After killing those Pinkies, another wave of 4? Pinkies (etc) is
   triggered.

   After the fight, visit the Auto-Map, and get the CODEX ENTRY "UAC
   Personnel / Dr Samuel Hayden 2".

   There's also a Health Station here.

   After triggering and watching a holographic replay, you'll be allowed out
   the Security Station's second door.

Mission 7: Fight: Exiting Security Station

   Opening the door, you'll see a Pinky: but there's actually 2 Pinkies. As
   well as 2 Revenants, 2 Imps. You can use the Quad Power-Up but I usually
   save it for the more tough fight coming up. Once you kill all these guys
   you'll get a CHECKPOINT.

   There's ELITE GUARD 7.3 on the top level.

   Interact with the Munitions Crate in the far corner of the lower-level.
   Unfortunately you'll need to re-do this each time you die: on the positive
   side, this Munitions Crate refills between most battles.

Mission 7: Fight: Exiting Security Station and Entering ???

   This fight is triggered when you take the stairs across the chasm after
   killing everyone.

   Initially there just a lot of The Possesseds staggering around, but a
   Revenant, an Imp, and a Cacodaemon are the first wave of guests to this
   party.

   A second wave (somewhat indistinct), is another Revenant, Cacodaemon and a
   few Imps.

   The third wave is different: two Pinkies and a Mancubus. These guys come
   out of the hangar ahead of you, and if you time it right, you can take
   them out with a single satisfying Quad-Damage Siege Cannon on the bridge.

Mission 7: Fight: Indoor Gore Nest

   Enter the building picking up health, Gas, Plasma, and CODEX ENTRY
   "Monsters / Mancubus 3".

   Almost the entire pre-fight can be handled with a single Gauss Cannon
   Siege Mode shot. Except you may have to deal with a pernicious Hell Razer,
   plus a lurking Possessed Security (use the Gauss Cannon on this fool, who
   hides on the left as you approach the Nest).

   Before destroying the Gore Nest:

     * Consider taking the Megahealth Powerup on the crate above.
     * You'll probably want to use your chainsaw, so find Gas where the
       Possessed Security hides (to the left as you initially walk toward the
       Gore Nest).
     * The two Pinkies spawn in reliable locations, one near the entrance
     * I usually retreat toward the entrance to minimize complications and
       environmental risks: your mileage may vary.

   In addition to 2 Pinkies, a Hell Knight and a few Hell Razers spawn.

   The finale is a Hell Baron, who starts on the far side of the room (with
   the Health Station and chainsaw). I like to use the chainsaw on it, but
   the Gauss Cannon/Siege Mode is also quite effective.

Mission 7: Post-Fight ??? Cleanup

   Pickup all you can.

   There should be a screen prompting "Reset Crane to Base?" to access near
   the bridge over the electrically charged floor. Actuating the Crane will
   cause a large suspended block to move within jumping range. Jump onto it,
   then jump right onto a catwalk. This is SECRET 7.5: access FIELD DRONE 7.1
   at the end of the U-shaped catwalk. (I tend to choose Chain Gun / Mobile
   Turret here.)

   Exit through the door near the Health Station.

Mission 7: Accessing Rune Challenge: Armored Offensive

   Exit the building and turn left, killing an Imp and Revenant.

   Jump across to the right and follow the walkway to the end to find RUNE
   CHALLENGE 7.2 "Armored Offensive" (which is also SECRET 7.3).

   This is a useful Rune for hard fights, since getting more armor is the
   same as more health, for the most part.

   Now, turn around, and run back toward the waypoint. To the left you'll
   find a Munitions Crate on a plateau. Often there are The Possesseds
   stumbling around and even a Cacodaemon at times. After killing all that,
   you should find a CHECKPOINT.

Mission 7: Fight: Upper Gore Nest

   Continue along the ledge, jumping around to the green-lit ledges. At the
   top, you'll find an airship with some loot - including CODEX ENTRY
   "Monsters / Cacodaemon", a Hell Knight, a few Imps, and a bunch of
   Possessed worshipping the Nest.

   Kill the Hell Knight and the Imps, and use the Possesseds for target
   practice.

   When ready, destroy the Gore Nest.

   Immediately a Hell Knight will spawn behind you, and some Imps and Hell
   Razers.

   There will be 3 Cacodaemons and 3 Revenants over the course of the battle
   as well.

   Toward the end of the battle, a Mancubus will emerge.

   Use the Haste Powerup in the corner whenever you need a boost: this fight
   isn't too tough.

Mission 7: Post Upper Gore Nest

   ARGENT CELL 7.1: Looking back the way you came, you should see a plateau
   at your elevation: it is easy to get to. Once there, look down at see the
   Argent Cell: drop down to it and choose your powerup.

   Go back to the site of the Gore Nest, and enter the door.

   There is a Pinkie Corpse holding the Yellow Guard Corpse. You can interact
   with it to get the Keycard.

   There's also a secret here. Look up for a bloody ledge in the ceiling at
   the left of the room on entry. Find SECRET 7.1, COLLECTIBLE 7.2, "Baron of
   Hell Model, Patriotguy".

   Return to get the Yellow Keycard, watch the holographic replay, and use
   the Yellow Door.

   Drop down the elevator shaft. Before exiting the obvious way, turn around
   and look up to find a square duct: jump into it and find ELITE GUARD 7.4.

   Exit the elevator shaft: you should recognize this as the site of an
   earlier Gore Nest battle. Make a hairpin turn to the right and go in the
   Yellow Keycard Door.

Mission 7: Fight: Tram Access

   A few Possessed Soldiers and a number of The Possessed lurk here, useful
   for some Weapon Upgrade tasks. When ready, interact with the Tram Console
   to "Resume Route" to finish the level.

           Mission 8: Advanced Resource Complex "A Brighter Tomorrow"

   Notes on Combat Challenges:

     * Bottle Opener: quite easy as there's a lot of The Possesseds wandering
       around in non-threatening situations
     * Double Take: watch out! you can't do this in replay if you miss a
       Rune!
     * Hide and Seek: easy

Mission 8: Introductory Lobby (with small Fight)

   Enter a large lobby area, finding a Mancubus killing some The Possesseds.
   After killing these, look for a pair of restrooms. There's a GAS CAN in
   the main hallway. (In the Men's Restroom is some armor you can save for
   later maybe.)

   In the Woman's Restroom is a hatch allowing access to a secret area. Climb
   onto the sinks and look around for the bloody hatch: jump to it and follow
   the duct (there's another GAS CAN) to drop into a room (SECRET 8.7) with
   an Auto-Map and an ELITE GUARD 8.1. The screen next to the door will open
   it.

   After exiting the Secret Room, you'll enter a Security Area with 6? The
   Possesseds, a Health Station, an ARGENT CELL 8.1, a Plasma Gun, and a
   terminal to Release the Safety Lockdown: do that.

Mission 8: Fight: Main Lobby

   Exiting the security area, there's a handful of The Possessed to dispatch.
   Then a Possessed Soldier or two, and finally a Possessed Security and a
   Hell Knight in the main lobby area. Keep moving and focus on the meaner
   demons.

   Watch a holographic replay of Dr Hayden and Olivia Pierce arguing about
   her research. Meanwhile, pick up CODEX ENTRY "Environments / Advanced
   Research Complex 2" from the main desk. When you interact with the panel
   to open the main building, there will be a Checkpoint, so gather supplies
   before that - the upcoming fight can be a bit difficult.

Mission 8: Fight: Central Area of ARC

   The entryway contains 6 Imps worshipping or something. Use a grenade or
   whatever you need for weapon or rune upgrades.

   Drop down to the lower central area, where you'll find 6-8? The Possesseds
   worshipping a Gore Nest. Often, an Imp for above will escape and find you
   as you are down here: watch out!

   My strategy for the start of this fight: Destroy the Gore Nest; lob a
   grenade into the center where Imps are forming in front of you (this tends
   to be quite effective), do a U-Turn to find 2 Imps to blow away with Super
   Shotgun. A Mancubus has formed in the tunnel to your left: kill it with
   whatever means, including Chainsaw (there's more fuel in the central area
   near the Gore Nest's location).

   Once the Summoner comes into existence, grab the Berserk Powerup. In a mad
   rage you'll likely be able to kill nearly all the remaining demons, but
   focus on the hard to kill demons just in case, as possible.

Mission 8: Meeting Dr Hayden

   All the bad guys being dispatched, follow the in-game waypoint to Dr
   Samuel Hayden's office.

   POINT OF NO RETURN: You can't come back here, so if you are missing the
   Auto-Map or the Elite Guard, get them now. (??? check that they're even
   still available post-fight?)

   Dr Hayden will resupply you to a large extent (he could really use a Mega
   Health but whatever). He will also explain about the "Helix Stone" and Dr
   Pierce's private lab "across the chasm". Finally he directs you to the
   service elevator: classy.

   The Dr is in no mood for futher conversation, so take the service
   elevator. When the door opens, find CODEX ENTRY "UAC Personnel / Dr Samuel
   Hayden 3".

Mission 8: Moxim Service Bay

   The olive green area has 4? The Possesseds. Kill them and find ELITE GUARD
   8.2 in this area.

   Continue along to get charged by a Possessed Engineer.

Mission 8: Fight: Gore Nest 1

   This fight takes place in a small-ish pit area. There's a Haste Powerup.

   The pre-fight is all Possessed Engineers and is unlikely to be a problem.
   Often they materialize rather late anyways. ???

   The initially a Cyber-Mancubus appears in front of you; then 2 Mancubi;
   then another Cyber-Mancubus; along with 6? Imps.

Mission 8: The Chasm: Secrets Galore

   Go to the marker indicated by the game, and interact with the screen to
   "Lower Security Field".

   First, there's the RUNE CHALLENGE 8.1 (SECRET 8.8). Look out onto the big
   chasm and turn 90 degrees left to find an airlock. Use it to access Rune
   Trial "Blood Fueled" (I personally don't use this one). There also a suit
   of armor.

   Second, there's the Classic Doom Level, SECRET 8.10. This jump to the
   lever is pretty tricky.
   Jump across to the immediate platform, and turn left and drop onto the
   platform below the Gas can. Turn around and look to the left to see a
   green light-bar, indicating a platform you can jump to. Keep going around
   this rock and jumping up: the top has a suit of armor on it. From this
   top, look directly opposite from the entrance area. You should see some
   pipes and a lever at your exact elevation: you need to jump there. The
   trick is that there is an invisible ledge about 12' (4 meters) below the
   level. If you land on that it is confusing: but if you have the In-Flight
   Mobility Rune you should easily be able to jump from this awkward position
   to the Lever. The upgraded In-Flight Mobility Rune helps too (make sure to
   activate it).

   (It is also possible to access this switch from the platform near the
   megahealth described below. It's perhaps a bit easier.)

   Third, from the Lever, face the piping and jump onto the pipe. Duck and
   turn into the cave, and search around into you find SECRET 8.6,
   COLLECTIBLE 8.1, "Supershotgun Model / Phobosguy"

   From there, look out for Lost Souls, and jump around until you get where
   they suit of armor was (on top of the rock). From there, jump back toward
   the entrance, and keep going that direction to find the Classic Doom Level
   (SECRET 8.10)

   Fourth, go, yet again, to the high point where the suit of armor was. Look
   for a lower pinnacle and jump there. From there, it is about a 45-degree
   right-turn to the Mega Health Powerup, SECRET 8.5. Once you get this
   powerup, a Cacodaemon will rise to attack you.

   Fifth, from where the Cacodaemon appeared, look for a bay opening. It
   contains an ARGENT CELL 8.1, SECRET 8.4.

   Finally, look for a hatch that is opening and closing (the in-game
   waypoint should lead you here). Jump down onto it for an irreversible
   Checkpoint.

Mission 8: Twin Intake Area

   Here we are in a pair of air intakes. If you look around you should see a
   Field Drone behind a grate: it is actually in the space directly in
   between the twin intakes. But it must be accessed from the other side.
   Jump onto one of the rectangular panels, and jump onto the only walkway.
   You should see a green-lit hatch to jump to. We want to get to the top of
   the air intake: we could do it here, but we should access the Field Drone
   first.

   So, walk through the tunnel: an Imp will jump out.

   Keep going: you'll get to the other intake. Turn it off using the panel,
   and jump down the hatch (just like the one you came up). You should find a
   shaft with FIELD DRONE 8.1 in it.

   Reverse your steps, and turn the air intake back on. Step in, and enjoy
   the ride up!

   Climbing up you'll get to a 4-way shaft intersection: directly in front
   and in back of you are each of the twin intakes. The in-game waypoint
   points you toward BFG Labs Lobby. The other direction has some armor if
   you need it.

   Proceed toward the in-game waypoint, to a lobby. This area has TWO green
   door: the big one directly in front of you with the waypoint, and a
   smaller door to the left housing SECRET 8.3: ELITE GUARD 8.3.

Mission 8: Fight: The BFG Labs Access Hallway

   Now, go forward into the ring of labs in the BFG complex. Get a big gun
   out and shoot 5 Possessed Soldiers, 2 Possessed Securities, and 1
   Cyber-Mancubus.

   I usually use a super-shotgun to start, then a mix of rockets and gauss
   cannon to finish the Cyber-Mancubus.

Mission 8: Notes on the BFG Labs

   Let's look at the labs on the outside of the hallway-ring.

   I'm going to go clockwise (as seen from above) starting at the Yellow
   Door.

     * Yellow Door: find a Torso whose retina will grant you access to the
       BFG itself
     * Bluish Door "Prototype Lab 02". 4 The Possesseds.
     * Red-lit Door-ish area: there's a corpse, a Gauss Cannon and some
       plasma fuel.
     * Bluish Door "Prototype Lab 01". 4 The Possesseds. Once these guys are
       dead, stand on the machinery and look for an open duct. SECRET 8.2,
       COLLECTIBLE 8.2: "Pinky Model: Pinkguy" ??? Follow the duct to drop
       into a room with a The Possessed, plus CODEX ENTRY "Weapons /
       BFG-9000". Go out this door into the main circular hall

   That's it: now go to the in-game waypoint and interact with it.

   You can probably figure out how to get the BFG from here, but the next
   section will spare no details.

Mission 8: Accessing the BFG (Defeating the Security Measure)

   Enter the chamber; the alarm will sound, i guess it noticed that the
   retina was attached to a corpse. Anyways, jump onto any of the symmetric
   metal platforms (on the walls), and watch the crazy security apparatus.

   After about 10 seconds, a sequence of lamps will light up and you can to
   shoot the obvious cells (you need to shoot 4 of the 6 cells). Do so, and
   the security system collapses and you can claim the BFG for your arsenal.

   Watch the cut-scene.

Mission 8: Fight: Test The BFG

   This fight is designed to be a nice place to use the BFG, for casual
   players. But it's probably better to work on all kinds of Weapon Upgrades
   (Super Shotgun, Gauss Cannon-Siege Mode, Chain Gun-Mobile Turret).

Mission 8: Before heading out: Rune Challenge "Intimacy is Best"

   Watch the holographic replay.

   Before going ahead, go right through a newly green-lit door; turn left
   into a yellow-gold-lit narrow opening to SECRET 8.9, RUNE CHALLENGE 8.2
   "Intimacy is Best"

Mission 8: Gore Nest 2

   Now, charge forward into a battle designed to showcase the BFG (and you
   may as well use it, since you can only store 3 charges.)

   Prefight: use a few Siege Mode/Gauss Cannons to kill the incoming hordes
   from the Checkpoint. After that, coming into this area, 3 Lost Souls will
   spawn: one straight in front, one left, one right. After you learn where
   they spawn they are easy to deal with - and since you have to re-kill them
   every time you die in this battle, you'll probably learn where they spawn
   too.

   Now, destroy the Gore Nest. Use the most powerful weapons available.

   When you think you are done, it's a bit of a trap. You have NOT gotten to
   a Checkpoint until you kill the 2 Hell Barons that follow.

   A robotic voice will announce that the demonic threat level is reduced,
   but that is just a temporary reprieve: not a Checkpoint.

   However, one easy BFG blast will take care of both Hell Barons.

   To conclude the level, enter the elevator and "Exit Facility".

                       Mission 9: Lazarus Labs "Lazarus"

   Notes on Combat Challenges:

     * Variety is the Spice of Death II: note that glory kills on Hell Razers
       count as well.
     * Thread the Needle: use the BFG. There's two fights shortly after
       acquiring it that should reliably achieve this.
     * Time Well Spent: easy, but also easy to miss. Make sure you do it
       before leaving Olivia's back lab.

Mission 9: Intro

   Grab Gas, the CODEX ENTRY "Environments / Lazarus Labs", and recharge your
   health (you can't get back here). In the next room you can get the rarely
   used Siphon Grenade. Then jump down the chute.

   There's a number of The Possesseds, Possessed Soldier and Hell Razers
   (glory kill them different ways to work on the Combat Challenge), and a
   Pinkie.

   Following the waypoint, you'll remove a corpse-chunk that's blocking the
   elevator, and 3 Imps will jump out. Kill them, then use the Munitions
   Crate. The non-Secret flow is to jump into the shaft and open a grate.
   Instead, look behind the crates behind the Munitions Crate. There's a duct
   (SECRET 9.1): follow it to a Mega Health that'll drop you into the next
   fight.

Mission 9: Fight: First Warehouse

   A big fight, with many Hell Knights and Revenants.

   Kill all these guys, and enter the green-lit doorway.

Mission 9: More Secrets

   Go up some stairs in a red-lit area. Before continuing on, turn around to
   see a duct with shotgun ammo. Jump into the duct, and follow it to a
   grate, that you may open. Enter SECRET 9.5. Here is ELITE GUARD 9.1 and
   CODEX ENTRY "Database / Elite Guard 2".

   Now, continue toward the in-game waypoint. You'll pass through a
   transparent walkway while Dr Hayden tries to explain things. There's lots
   of activity outside.

   At the end of this walkway, find FIELD DRONE 9.1 (although you may have
   already gotten the good upgrades).

   You'll find yourself in a curving hallway with 4 The Possesseds, and CODEX
   ENTRY "Monsters / Cyberdaemon 2".

   Continue down the hall to a few Possessed Soldiers and a Hell Knight.

   Continue up a short flight of stairs and look for a white hatch in the
   floor right in front of you. Interact with it to drop with for SECRET 9.2.
   Climb up to find RUNE CHALLENGE 9.1 "Rich Get Richer".

   When done, actuate the screen near the door to exit - you'll be back at
   the hatch.

   From the hatch, go into the next room: there should be two large steamy
   windows in this relatively small area. Facing the windows (as you come
   into the room), look right for a torn duct you can climb into. Drop down
   into an area with the AUTO-MAP. Exit through a duct behind the columnar
   structure in the room. You'll come to an old school looking panel of
   lights. Jump up, and look for a grating to open, to exit back to an early
   hall.

Mission 9: Fight: Miscellaneous Hallway Guards

   The first room has a few Possessed Securities and many The Possesseds and
   a couple of Possessed Engineers.

   The second room has a CHECKPOINT (used for the next fight) and 4 Possessed
   Soldiers and a Hell-Razer. The next room has a bunch of ammo and a Health
   Station, then drop down the hatch to enter the next fight.

   POINT OF NO RETURN: Once you finish the next fight, you cannot get back to
   this tunnel area (so make sure you interact with Rich Get Richer, even if
   you don't solve it)

Mission 9: Fight: Mancubus Operating Room

   Many Possessed Securities, The Possessed, Hell Razers, Possessed Solders,
   3 Mancubi will spawn. Toward the end of the fight is 2 Hell Knights. I
   like using the Plasma Rifle Heat Wave with the Quad Damage to plow through
   the bad guys - but your mileage may vary.

   After the fight look at the empty mancubus bed at the back of the room,
   between the two exit doors. Behind this, is a screen you can actuate to
   find ELITE GUARD 9.2 in SECRET 9.4.

Mission 9: Fight: Stone Tablet Exhibit Hall

   There's a Munitions Crate in the entrance hallway to this area. Once
   you've looted the area, look through the door to see if you're going to be
   ambushed by a Possessed Soldier right next to the entrance. Open the door.

   This fight begins with 3? Possessed Soldiers (one is close-by and needs to
   be dealt with urgently) and a large number of The Possesseds (use a
   grenade or two maybe). (Here's your first good change to get the Thread
   the Needle combat challenge). Shortly, 2 Pinkies spawn at the back of the
   room.

   Killing those Pinkies will cause the spawning of 4 more Pinkies and a bevy
   of Imps. Use the BFG, Chainsaw, and general evasive maneuvering.

   Cheap Strategy: After killing the Possessed Soldiers, go into the tunnels
   behind the stone artifacts. The monsters (most conveniently, the Pinkies)
   cannot go back there, but Imps can still fireball you. You may need to
   chainsaw someone for ammo: the second Pinkie can be a good choice.

   Post-Fight: Going back to the entrance door of the room, and look at the
   stone tablet to your left. There is a gap you can use to enter some access
   tunnels: this is SECRET 9.3. In the back, find COLLECTIBLE 9.1 "Olivia
   Pierce Model, Eliteguy".

   There's also a Mega-Health you should take before leaving the backstage
   area. (Hint: equip Rich Get Richer before taking the health to get one of
   the Upgrades)

   Cheap Strategy for upgrading the Rich get Richer Rune here: If you don't
   use the Mega-Health during the fight, then you can obtain it repetitively
   after checkpointing. But you'll have to die in order to reset the
   checkpoint. (the cheap strategy is not appealing anymore since a non-dying
   strategy is available in Titan's Realm.)

   Press the screen as indicated by the in-game waypoint. Enter what looks
   like an elevator to transfer you to the Lazarus Archives.

Mission 9: Accessing the Helix Stone

   This really just involves interacting with a few screens, in all cases,
   the in-game waypoint takes you there.

   SECRET 9.6, COLLECTIBLE 9.2 "Samuel Hayden Model, Toxicguy" is found in
   the circular archive room. Look on the upper floor for a red display
   screen (there's another similar display in a cyan color: ignore it).
   Behind it, a single archive cell's light is red -- all the other lights
   are yellow. Interact with this to obtain the doll.

   The anteroom to Olivia's Lab holds CODEX ENTRY "UAC Personnel / Olivia
   Pierce".

   After a few screens, you be in Olivia's Private Lab: there's a central
   hologram of a stone coffin-like thing being guarded. There's BFG Ammo, a
   Munitions Crate, an ARGENT CELL 9.1, and a screen to interact with. On the
   left is a lone dilapidated computer where Demon Destruction can be
   "played": just interact with the running computer on the side and exit to
   get the Combat Challenge.

   The final screen is back in the circular archive room: be ready for a
   fight after Dr Hayden rambles on a while.

Mission 9: Fight: Circular Archive Room

   Be prepared for a endless Imps and a long sequence of Hell Knights. An
   Mancubus will spawn; and toward the end, 2? Cacodaemons.

   After dispensing with all the demons, a circular stairway drops down from
   the center of the room.

Mission 9: Fight: Small fight in Bloody Temple / Pew Area

   A few Possessed Securities and a bunch of The Possesseds linger about this
   gory area.

   When cleared, there will be a hologram of Olivia watching over a
   ritualistic sacrifice.

   There's armor behind you as you stand in the entranceway to this area.

Mission 9: Circular Hatch Room

   Exit to the right to a blood-strewn corridor with books and candles.

   You will get to a circular room with a pit in the center. Looking in, you
   can see an Elite Guard, but before that, look right for a Lever to access
   a Classic Map.

   Now, jump in (SECRET 9.7) and get ELITE GUARD 9.3 and SECRET 9.8, CLASSIC
   MAP 8.1 "Doom - Tower of Babel".

   Jump back out, and go to the screen with the waypoint: "Cycle Hatch".

   Do this, and jump onto the platform while it is plugging the hole. Wait
   for it to lift you up, like an elevator.

   Drop down, and keep going and you'll get to a yellow-lit door labeled
   "Maintenance Only". Enter for a fight.

Mission 9: Fight: Server Hall

   You catch a few Possessed Securities off-guard, use grenades etc. There's
   also a Pinkie ahead of you in the hallway. And a few more The Possesseds -
   including some that may surprise you by popping up.

Mission 9: Server Hall

   The hallway become increasingly bloody, and you finally open a door onto a
   console area. A hologram with Olivia is playing, and you must interact
   with a terminal at the waypoint here, the energy refractor control. It
   opens the twin doors.

Mission 9: Fight: Two-Level Lounges

   Two identical hallways (with bloody skeleton wallpaper), take you to a
   symmetric 2-level area strewn with Imps, Possessed Soldiers but mostly The
   Possessed.

   Once cleared, from the entry, go to the lounge on the right on the
   upper-floor. Look around for a bloody duct at approximately head-height.
   It takes you to SECRET 9.9, RUNE CHALLENGE 9.2, "Saving Throw".

   There's also ELITE GUARD 9.4. Outside the door, in the non-secret area, is
   a Munitions Crate.

   Then go to the waypoint: a large silo with green concentric circles
   surrounding the waypoint itself.

Mission 9: Portal Area Fight

   The robotic voice announces demonic presence, but you won't see much. You
   have to enter the narrow hallway and go through the teleporter.

   Before doing so, equip In-Flight Mobility. Then enter the teleporter and
   jump back. You should land on a shelf instead of falling to the ground.
   This is the perfect place to use the BFG to get the Thread The Needle
   Combat Challenge: it'll make the fight much easier too.

   This is a good fight to use the Plasma Gun / Heat Blast - fight everyone -
   grabbing the Haste Powerup whenever you need health. Use another BFG if
   helpful - there's a few lying around. When the Pinkie or Hell Knights show
   up, grab the Quad Powerup: it (along with Heat Blast) should be easy work
   of the remaining heaps of demons.

Mission 9: Prepare for Boss fight

   Follow waypoints, grabbing supplies, along with CODEX ENTRY "Monsters /
   Cyberdemon".

   Dr Hayden explains that this fight will have two parts. The first part is
   the easier one.

   You will get 6 bonus Weapon Upgrade Points before the fight begins.

Mission 9: Boss Fight, part 1: Mars

   Here's the most notable Cyberdemon moves for the first part:

     * the Rockets: he'll launch a volley of horizontal rockets; so long as
       you keep moving you should be ok.
     * the Charge: things will slow as he prepares to charge, so get ready to
       jump away.
     * the Jumpable Laser Shot: this thing does a lot of damage so you really
       need to jump over it.
     * the Charged Laser: this multiple beam laser shoot from his arm. It
       starts red and intensifies to whitish-yellow before firing. You really
       benefit from the In-Flight Mobility Rune for dodging this - upgraded
       is better.
     * the Mortar Volley: he will launch a bunch of rockets upward; their
       projected landing spots will be on the ground - find a place in
       between them to stand. This attack is combined with a Charge, a
       Jumpable Laser Shot, or a Changed Laser.
     * the Sidejump: he will sometimes take a big jump to the side. This is
       his (pretty effective) move against slow Gauss Cannon and BFG
       enthusiasts: don't waste your ammo if you detect it.

   Recommended Runes: Vacuum, Ammo Boost, In-Flight Mobility. (notes: Armored
   Offensive is useless since he doesn't drop armor. Saving Throw is
   marginal. Rich Get Richer is good if you have 100 armor (unlikely). He
   stays staggered for a while, so Dazed and Confused isn't really helpful.)

Mission 9: Boss Fight, part 2: Hell

   A small cut-scene transports you to Hell; the Cyberdemon gives you the
   claw, and is reborn. You will also be pretty well charged up.

   He adds two new attacks to his repetoire:

     * the Triple Jumpable Laser Shot. The first shot will be low; the second
       high; and the third low. It just takes practice. Easy mistake:
       double-jumping the first laser and getting hit by the second.
     * the Double Wall. He makes a temporary corridor, which'll be combined
       with a Triple Jumpable Laser Shot or Rockets. To deal with the Double
       Wall with Rockets, move in a circular pattern using In-Flight
       Mobility.

   Same Rune Notes apply as above.

   Feel free to use all of your BFG ammo.

   You will get 2 Weapon Upgrade tokens.

   When the fight is over, jump into the red teleporter.

                   Mission 10: Titan's Realm "Titan's Realm"

   Notes on Combat Challenges:

     * Trick Shot: I don't know why, but using the Rocket Launcher's Lock On
       mode seems to achieve this reliably. There are other ways, but I
       haven't found anything as consistent.
     * Atop the Mountain: there's a number of fights that end with the Hell
       Baron. For some reason, i often accidentally kill them instead of
       staggering them. You have to jump from higher ground to do this! This
       fight where you get the Blue Skull is probably the easiest to get this
       on, because the Hell Baron starts in a pit.
     * Dominator: there's a Berserk Powerup that is your main helper here.

Mission 10: Introduction

   From the walkway, find CODEX ENTRY "Artifacts / Slayer's Testament #4".

Mission 10: First Fight

   Jump far down to a bloody pit to be immediately attacked by 3 Cacodaemons.
   As proceed up the stairs to be attacked by another Cacodaemon and a
   Cyber-Mancubus.

   Continue up the hellish path to a yellowish cave guarded by 4 Lost Souls
   and 2 Cacodaemons.

   CHECKPOINT.

   Enter this room: you should see a bridge over a pool of toxic sludge. If
   you look under the bridge, you can see a Skull Switch. Actuate it and get
   out of the sludge. Facing into the room from the entrance, this caused an
   alcove to open up on the toxic floor, right next to a green torch. Inside
   this alcove is SECRET 10.3. ELITE GUARD 10.1. And some armor.

Mission 10: Fight: Entrance Hallway

   Proceed, triggering the creation of some Lost Souls, some Hell Razers and
   a Pinkie.

   Proceed to the right. When you grab the suit of armor, it'll trigger 2
   Hell Knights to instantly appear. There are also 4 Unwilling in the next
   room, along with a Skull Switch: press it.

   This'll trigger the spawning of a Cyber-Mancubus, which will end this
   fight.

   CHECKPOINT.

   Now, pick up loot and search around for the FIELD DRONE 10.1, SECRET 10.2
   (it was visible before so it may be on the map).

   Proceed to the next fight: the target will be a gated-off green
   teleporter, but some demons will distract you en-route.

Mission 10: Fight: First Teleporter

   Upon entry to this complicated arena, a Cyber-Mancubus will spawn off to
   your left, and a Mancubus will spawn in the area in front of you. Polish
   them off however is convenient.

   A gaggle of other daemons come along as well. A few Imps, few Revenants, 2
   Pinkies.

   Use the Haste since this is the only fight in this area - use it to work
   on the Dominator Combat Challenge.

   Once you get the CHECKPOINT, approach the Teleporter and the bars will
   lift. Enter for an iconic fight.

Mission 10: Fight: Bloody Cave

   Dave's Opening: I usually turn right coming out of the Teleporter, picking
   up shotgun ammo and a suit of armor. Look left into a cave before a Yellow
   Lift: there should be Rockets on the ground and a Quad Powerup in the
   background. In a few seconds, a Mancubus will appear right on the rockets:
   lob some grenades and go up the stairs right past the Yellow Lift. You
   should find a Gas can, and down the hallway, the only Pinkie in this
   fight. Kill it and then run and fight as usual.

   The finale is 2 Hell Barons. I often save the Quad Powerup for them (note
   that 4 Imps spawn when you take the Powerup).

   Post Fight: the map may have a doll on it: SECRET 10.1, COLLECTIBLE 10.1
   "BFG-9000 Model / Keenguy". If not, it's in an alcove of the entrance
   wall.

   Follow the in-game waypoint to the teleporter. You'll arrive at the
   Auto-Map, use it.

Mission 10: Fight: Rectangular Pit

   After 6 Lost Souls, deal with 4? Hell Razers and a bunch of Imps. They can
   be mostly killed just by shooting barrels. Use the Rocket Launcher on the
   Lost Souls to get the Trick Shot award or kill them however you want.

Mission 10: The Yellow Skull and its Door

   Post fight: look for a Yellow Lift near the red door to get you onto the
   rafters. Across the way is a yellow pyre: jump to it for SECRET 10.4,
   COLLECTIBLE 10.2: "Cyberdemon Model, Silverguy". Jump back.

   Now jump over to the landing with the green suit of armor and a
   wood-grid-patterned door. It'll open and you can take the Yellow Skull.

   But! It's a trap. A very easy obvious trap. I think you'll figure it out.

   Continue through the hall (in the direction of the greenish area with the
   gibbet - the area you haven't been to yet).

   A grate will appear to block access to the yellow door.

   So, you must go left into a toxic area with a bunch of Unwilling
   staggering around. You will see an Invulnerability Powerup here, and at
   the end of the corridor, an ELITE GUARD 10.2 and a Skull Switch. Activate
   the Skull Switch.

Mission 10: Fight: Toxic Sludge Area

   On return, two hatches will open exposing 2 Mancubi. You can use the
   Invulnerability on them, or fight more carefully and save it for a minute.

   Once they are gone, take the Invulnerability if you haven't and run up the
   stairs to fight 3 Pinkies.

   After that, the Yellow Skull Door is accessible, and a CHECKPOINT.

   Before going through the Yellow Door, though, note that another passage
   has opened and get ARGENT CELL 10.1 and CODEX ENTRY "Monster / Pinky".
   (Actually, if you want to get the Rich is Richer upgrade, I recommend
   waiting for after the following fight)

Mission 10: Fight: Pounding Rock Area

   The Yellow Skull Door opens to reveal what appears to be a red skull
   switch, but it's a trap: the floor drops out and suddenly you are fighting
   a Mancubus, then 2 Revenants and a Hell Knight with some Imps in the
   background.

   At some point, 2 more Mancubi and a Cyber-Mancubus spawn as well.

   Note that there's BFG ammo here, so if you are full, feel free to use it!

   NOTE: the nearby acid pools allow you to reliably inflict just 1 point of
   damage, which makes this area very convenient to get the Rich Get Richer
   Rune upgrade. In order to do that, do NOT pick up all the armor during the
   fight, you want about 4-8 stray armor left, at least.

Mission 10: Pounding Rock Area

   When the pounding rock is down, quickly climb onto it. It'll lift you up
   to a Skull Switch: press it, and drop down.

   Before continuing, to toward the Yellow Door, which is currently gated
   off. Look for a small alcove continuing the Classic Doom Map Lever. Pull
   it. The gate to the Yellow Skull Door will open: go that way and go back
   to the lower Toxic Sludge room (where the Mancubi appeared with the Elite
   Guard), and you'll find CLASSIC MAP 10.1 "Phobos Anomaly": SECRET 10.5.
   This area also has a Mega-Health: Go down a corridor and interact with a
   discolored wall-panel on the right-side to get the Mega-Health.

   Go back to the Pounding Rock Area. Go toward a gated off green teleporter.
   Look left to see a large room with 2 Yellow Lifts and a Suit of Armor in
   the middle.

   Go in to what I call the Treasure Room, and pick up some loot and a Blue
   Skull, a fight is triggered on the way out.

Mission 10: Fight: Treasure Room

   It starts right near the entrance/exit with 3 SPECTRES. This is quickly
   followed by some Imps and 4 Lost Souls. Then 2 Cacodaemons and 3 Mancubi.
   Finally, a Hell Baron.

   CHECKPOINT.

Mission 10: Segue

   Now, after checking for stray supplies, enter the green teleporter (the
   bars will disappear as you approach).

   You'll be in a fiery yellow lit area.

   Grab CODEX ENTRY "Artifacts / Slayer's Testament V". Turn left for SECRET
   10.6: a Mega Health (don't forget Rich Get Richer upgrade).

   Continuing along, you'll be back at the Rectangular Pit.

Mission 10: Fight: Rectangular Pit, Blue Skull Door Fight

   A Berserk Powerup has been placed for this fight. It starts with many Imps
   and also include a 3 Hell Knights, 2 Summoners, a Mancubus. It ends with a
   Hell Baron.

   Use the Blue Skull, and find immediately on the floor CODEX ENTRY "UAC
   Personnel / Olivia Pierce".

   Jump into the red teleporter.

                           Mission 11: The Necropolis

   You find yourself in a central area of this level with the Yellow and Blue
   Skull doors adjacent.

   Notes on Combat Challenges:

     * A Pin Pops a Balloon: there are two clear opportunities for this.
       Right at the beginning, and after crossing the floating islands with
       Cacodemons. Try both, since it can be pretty easy to kill the Mancubus
       accidentally. Dazed and Confused Rune can help a little as can ???.
     * Two Mouths to Feed: when you cross on the floating islands there's an
       easy place to get this. Use Gauss Cannon / Siege Mode or BFG.
     * Wait For It: By kicking the first barrel down the steps you can get 3
       there; and the pre-fight in the Square room has 6 Possessed that are
       easy to get. There's a number of other chances if you don't die on
       those scenes (the kills count even if you die!)

Mission 11: Yellow Skull

   To your left at ground level is a teleporter. Jump into it.

   Find CODEX ENTRY, "Monsters / Cyber-Mancubus".

Mission 11: Fight: Yellow Skull Prefight

   Continue along to a barrel at the top of the stairs, if you kick it down
   you can shoot it to kill some demons, for the Challenge.

   Descend the stairs and quickly look back to shoot 2 Lost Souls. A Mancubus
   appears at the top of the stairs: he's a good one to use for the Pin Pops
   a Balloon Challenge. If you climb the stairs, 2 more Lost Souls appear.

Mission 11: Treats

   A CODEX ENTRY "Artifacts / Slayer's Testament #6", Gas, and ARGENT CELL
   11.1 (the last) are found by continuing down the corridor.

Mission 11: Fight: Traps

   Go back up the stairs to where a gate has opened: you should see a Skull
   Switch straight ahead in the next room, but as you approach it, a bunch of
   Unwilling and a Spectre spawn.

   Kill them and actuate the switch, causing 2 Hell Knights to spawn as you
   return. Go back down the stairs and kill a Cyber-Mancubus.

   CHECKPOINT.

Mission 11: Fight: Square Arena

   This is a square torchlit bloody room with 4 big pillars.

   Prefight: there a bunch of Unwilling roaming about and barrels: use them
   to work on the Wait for It Challenge. It's your best opportunity.

   After pressing the switch, the fight proper begins.

   3 Cacodaemons spawn, 2 Hell Razers and some Imps and 2 Spectres in quick
   succession. Then 2? Hell Knights and a Summoner.

   Grab the Auto-Map, pull the Classic Map Doom Lever, and grab the Yellow
   Skull.

   CLASSIC MAP 11.1 "Doom - House of Pain" is SECRET 11.3. Go back outside
   this room and down a hall to an area that looks funky on the map.

   This will trigger the teleporter to open, and you can take it to return to
   the central room you started in.

   On the opposite side, a new Teleporter has opened. This one will get you
   the Blue Skull.

   Go through the teleport for the next fight.

Mission 11: Fight: Four Platform Arena

   Soon upon entering, 2 Mancubi form on 2 of the platforms (two Gauss Cannon
   Siege Mode blasts will take both of them). Then 3 Cacodaemons and Imps.
   Then some Revenants and a Hell Knight ends this wave.

   The gates surrounding the Quad Powerup lift and 4 Revenants spawn, one on
   each side of the square. Then 2 Cyber-Mancubi and 2 Mancubi spawn: the end
   of the fight.

   Take the Blue Skull. Teleport back to the Central Room.

Mission 11: Fight: Central Room

   Use both Skulls, an interact with the knobs behind each door to trigger
   the next battle.

   3 Imps spawn in reliable location.

   2 Pinkies are next.

   2 Revenants, a Hell Knight and ? Spectre make up the next wave.

   The final wave is 2 Hell Barons.

   After the fight, two stair cases open up below the main area (see map), go
   there and drop into a small hallway with some health and another drop.

Mission 11: Fight: Cacodaemons in Air

   When you stand up from the jump, there will be 3 Cacodaemons lurking
   around.

   Use BFG or (better) Gauss Cannon Siege Mode to get the "Two Mouths to
   Feed" Challenge.

   Jump onto the next platform, which has two large unlit torch/pillars on
   it.

   The next platform has just one torch/pillar. Peer carefully down from the
   edge to see a small island. Sometimes you can catch sight of it from
   above, but often you cannot, but there is a doll on it. In-Flight Mobility
   helps (but is not necessary) to jump down there. This is SECRET 11.2,
   COLLECTIBLE 11.1 "Chainsaw Model, Tealguy".

   Continue hopping to the cave, where you will be greated by a Mancubus.

   Don't forget to get ELITE GUARD 11.1, and there's some armor too.

   Continue along to some shotgun ammo and the last FIELD DRONE 11.1.

Mission 11: Fight: Big Battle In-Progress

   Go up the stairs so where some big demons are duking it out: 2 Mancubi,
   some Revenants, Imps, and a Cacodaemon. Help them kill eachother and kill
   the Hell Razers, 2 Cyber-Mancubi and whatever else spawns. There's a BFG
   and a Haste Powerup.

   You'll want to get in good shape for the next fight.

Mission 11: Fight: Paired Hallway

   The same demons will spawn on each end of this hall. I'll give total
   numbers:

     * 2 Hell Barons
     * 2 Mancubi
     * 4 Spectres

   There's quite a bit of ammo around, and ELITE GUARD 11.2.

Mission 11: Fight: Last Non-Boss Fight

   Exiting, 2 Cacodaemons will immediately stalk you: kill them with the
   rocket launcher: there's ammo around.

   Walk down to the treasure trove with a big armor. This will trigger 2
   Mancubi to spawn. Retreat back to the original area and use Rockets, Gauss
   Cannon. Once you kill a Mancubi, 2 Hell Barons will spawn. Gauss Cannon or
   BFG is recommended: it won't take long for them to get to you.

   Now, you can get an obscure secret, SECRET 11.1. Look at the large statue
   / structure that is shaped like the head of a horned screaming demon. In
   its forehead, is a glowing pink rune symbol. Shoot it (with Gauss Cannon
   or Rocket Launcher or Assault Rifle/Tactical Scope, since you need range),
   and a weird cubic capsule will spit out of it and land next to you. This
   is COLLECTIBLE 11.2 "Gauss Cannon Model, Hazmatguy".

   Stock up, there are two Boss Fights coming up.

Mission 11: Boss Fight 1: Hell Guard

   This fellow has a force field (the transparent green sphere) that'll
   protect him from everything, even BFGs, so you must time your shots for
   when the field is down. Most of his attacks give you an opening.

   His moves:

     * Club Attack. He comes at you, move and aim, since his field is down as
       he attacks, and right afterward.
     * Charged Club Attack. Similar, but he puts more into it and damages
       everything is a radius (which briefly flames up).
     * Tri-Sphere Attack. He blows up a glowing yellow sphere, which briefly
       flashes, then turns almost white, then 3 very damaging shots are
       launched out. This can only be attacked after blinking but before
       shooting. The good news is that it stuns him for a bigger (Siege or
       BFG) secondary attack.

   Midway through the fight he gains some new tricks:

     * Spinning Flaming Spiral. Avoid the flames: after this he'll be
       attackable for an unusually long window.
     * Three Drum Waves. He beats the ground creating a relatively slow
       moving wave that does a lot of damage.

   Toward the end, you may wish to equip Dazed and Confused, since he doesn't
   stay staggered long, and you have to Glory Kill him.

Mission 11: Boss Fight 2: The Twin Hell Guards

   These guys really act in concert, but it's easier to describe their moves
   separately. They lack the force-field, fortunately.

     * Bed of Fire. One runs creating a sequence of long fireballs. Just jump
       over them.
     * Fire Tornado. One spins creating a whirlwind of fire. Avoid.
     * Sphere Attack. Like above but it doesn't flash or trifurcate. Shoot it
       right after it finishes inflating to stun him.

   When one is stunned, you can often line them up to get double damage out
   of Siege Mode or BFG.

   When they are getting low (20%), switch on Dazed and Confused so that you
   will have an easier time Glory Killing them.

   You will get 2 Weapon Upgrade points for killing these guys.

   After killing them, access the Crucible (which looks more like a dagger
   with a Skull at the top).

                      Mission 12: VEGA Central Processing

   Notes on Combat Challenges:

     * Variety is the Spice of Death III: there's a lot of Imps, including 4
       right soon after entering the building. Possessed Engineers also can
       be glory-killed to satisfy this requirement.
     * Gore Pinata: Plenty of opportunities for this as well. (The Equipment
       Rune and its upgrade help quite a bit)
     * My Teeth are Sharper: you can jump and chainsaw if needed.

Mission 12: Intro

   Enter either door, and in the Console area look for CODEX ENTRY "UAC
   Personnel / VEGA".

   Proceed to open the airlock, and get Gas or Ammo if you want it. Stop
   about 115 meters shy of the waypoint. Look for a green-lit Mainenance
   Hatch. Enter it instead of going to the waypoint.

   In one shaft here find COLLECTIBLE 12.1 "Hell Guard Model / Quakeguy"
   (SECRET 12.1) and a BFG ammo in the next shaft. Drop into the main area
   from the first shaft, possibly conservatively since there's about 5 Imps
   in there.

   Another Maintenance Door at ground level is followed by a green-lit hatch
   in the floor.

   Drop down to the area with the Security Switches.

Mission 12: First Switch Fight

   Many Imps, Possessed Soldiers, and Revenants spawn when you activate the
   first switch (the second switch doesn't trigger any spawning).

   This multistory area has many pickups, and the area is reused for the next
   fight.

Mission 12: Security Shutdown Fight

   Flipping the second switch does not cause any new demons to spawn.

   But, disabling security does cause 2 Cacodaemons and a Cyber-Mancubus to
   spawn. This fight can be won in a single BFG shot if you venture forward
   about 5 seconds after disabling the security system.

Mission 12: Cooling Access Fight

   Note: you can use the Berserk from the earlier fight.

   A few Possessed Securities and 3 Pinkies and a Mancubus scattered across
   about 4 rooms. A Health Station and CODEX ENTRY "Monsters / Revenant" are
   found near eachother. There also two Elevator Shafts off to the side that
   have 2 Possessed Soldiers and a BFG ammo.

Mission 12: Finding the Blue Keycard

   Back near the Health Station look for a very bloody side area with
   entrails hanging from the ceiling and a chainsaw. Enter and look for a
   hatch.

   Drop down to find a bunch of Possessed Engineers, The Possesseds, and 2
   Spectres.

   But most importantly, the Blue Keycard.

   Go through the Blue Door.

   Turn Left to find the Auto Map (if you haven't already), and continue in
   through another Blue Door.

   You'll find a SECRET 12.2, ELITE GUARD 12.2 here, and get surprised by a
   Revenant.

   Behind the crate that the Guard is leaning on is a Lever: pull it to open
   access to the classic doom level. Then go back past the Blue Keycard guy
   and look for a nested pair of crude circles on the map. That is SECRET
   12.5, CLASSIC MAP 12.1 "Doom - Command Control".

   Look down the shaft the Revenant popped out of. You'll see a Mega Health,
   drop down, making sure to get it.

   You should be standing on a rectangular duct in a very large icy tunnel.

   Drop down the other way for SECRET 12.3, COLLECTIBLE 12.2: "Cyber-Mancubus
   Model, Jungleguy". Walk along the duct to get back up. Enter the door to a
   tunnel.

   It'll drop you into a lobby where a holographic guy is blathering about
   how much energy they use.

   Continue on.

Mission 12: Fight: Coolant Generator Room

   Four Switches must be destroy (by shooting) to reroute the energy. It
   doesn't seem to matter much what order you go in.

     * Switch 1: 2 Cacodaemons and a Summoner spawn, and a long parade of
       Possessed Soldiers and Hell Razers and a few Imps.
     * Switch 2: A Hell Baron, 2 Pinkies, another Summoner, 4 Lost Souls.
     * Switch 3: Imps, Possessed Soldiers, Hell Razers
     * Switch 4: Nothing new spawns :)

   After the Demonic Presence is eliminated, and you have taken all the
   remaining loot, go to the waypoint and actuate the screen.

   Cheesy Strategy: You can hide behind lowest switch: eventually Pinkies
   will gang up on you, but then you can take advantage of the Berserk
   Powerup in the tunnel leading out of the area. So, the way I usually do
   the fight is go left past one switch, then go right and jump up across the
   gap to the second switch. Use Tactical Scope to take out the first 2
   switches from the same vantage. Then go outside and jump down to the 3rd
   switch; sometimes a Cyber-Mancubus will spawn there before you jump:
   either chainsaw him or go over/around. Destroy the 3rd switch and hide
   behind it, shooting out with the Gauss Cannon / Siege Mode etc. At some
   point, grab the Berserk. The cool thing about this is that the monsters
   mostly fight each other.

   There's also CODEX ENTRY "Monsters / Cyber-Mancubus" in this room.

   Follow VEGA's suggestion to jump down onto a train below to enter the last
   big battle on Mars.

Mission 12: Fight: Finale

   This takes place in a large depot area, with a few BFG Ammo, Gas cans, and
   other supplies littered about.

   You'll ride the train in and a well-timed BFG can take 2 Cacodaemons and
   the 2 Hell Barons plus a whole lot of random demons. Fire it at the 2 Hell
   Barons, just as the Cacodaemon at left is about to go out of view.

   The next wave consists of a few Cyber-Mancubi, 5? Pinkies, and 3?
   Cacodaemons, along with many Imps.

   There are 3 BFG ammo here - so you'll probably want to use it a few times.

Mission 12: Destroy VEGA

   A waypoint leads to a platform that'll carry you up to ???.

   But first, look down below for another platform to jump onto. Jump onto a
   ledge which should have SECRET 12.4, ELITE GUARD 12.3 on it (as well as a
   Munitions Crate).

   Take the elevator back up to the platform.

   Wait on it, until you get to a dramatic platform area.

   Disable the Neural Networks on the left and right. You will get 5 bonus
   Weapon Upgrade points after this is done.

   Then go to the center console. Pick up CODEX ENTRY "Environments / VEGA
   Central Processing". Then interact with the screen to get a cut scene that
   ends the level.

                            Mission 13: Argent D'Nur

   Notes on Combat Challenges:

     * Hold Still: only the third fight is good for this, so be careful that
       you have both Barons in sight when you use the BFG. It would be
       difficult to use the Gauss Cannon to achieve this.
     * Uncharted Territory: follow the guide.
     * Big [REDACTED] Gun: you'll probably get this without trying; you
       probably want to enable Ammo Boost II a lot to get even more BFG ammo.

Mission 13: Introduction

   You start in a large upper courtyard area with loot scattered about.

   Eventually, go down to a CHECKPOINT for the fight.

Mission 13: Fight: Sniper then Berserk

   You should start at an overlook, where you can see a Cacodaemon attacking
   a half dozen Imps. I usually kill the Cacodaemon (Assault Rifle with
   Tactical Scope) from afar and save the Imps for up close.

   Jump down to the courtyard area below and polish off the Imps who will
   come to you. The next wave won't start until you enter the main area.

   In short order, 2 Hell Knights and a Summoner appear, followed by 2
   Pinkies and many Imps.

   I usually use one BFG after lots of demons have spawned, then grab the
   Berserk Powerup from the very center of the courtyard.

   In theory it seems like the "Seek and Destroy" and "Savagery" Runes would
   may the beserk powerup more effective - I didn't really notice a
   difference though.

   When done, exit via the waypoint and CHECKPOINT near the blue teleporter.

Mission 13: Fight: Intro Stairs

   Before starting, look ahead to an impressively demonic sight of 3 statues
   feeding some central thing. (I'm not sure if the 3 beams symbolize the 3
   major fights ahead or not)

   Descend to the next level where there is usually between 1 and 3 Unwilling
   staggering around (they will fall down to the next level but they can't
   get back up, so the exact number varies).

   (Because I often seem to need the Mobile Turret upgrade, which involves
   killing in groups of 4, i often wait to kill them, but the Secret has to
   be triggered before you drop down to the next area)

   Facing out toward the canyon, look for a Skull Switch at the right-side of
   the level. Actuate it, then go to the other side of this area and look for
   some blocks to climb up. After climbing up, there is a cave just a bit
   ahead that opened up with Gas and BFG Ammo: SECRET 13.3.

   Go back down to the lowest area in this complex with about 8 Unwilling.

   Optional: go through the tunnel to the left. Once you take any armor at
   the end of the tunnel a Cacodaemon will materialize directly in front of
   you, and 2 Imps will appear in the hallway. A few seconds later a Hell
   Knight will appear at the far end of the hall (the entrance). (I usually
   use Gauss Cannon Siege Mode for the Cacodaemon and the Hell Knight -
   separately - and super shotgun for the Imps, but there's many options.
   Using a chainsaw on the Hell Knight could make things easy and give you a
   lot of ammo)

   Optional: go the other way (a right turn, if facing the canyon), to a
   rocky set of stairs leading up to the Auto-Map for this level.

Mission 13: Fight: Stragglers on the Islands

   Jump across the gorge: keep an eye out over the canyon where 2 Lost Souls
   and then a Cacodaemon will spawn.

   Jump down and across the canyon.

   Go left and turn around to see the next jump.

   2 Cacodaemons will appear, one at at time, after you jump across.

   This island has two levels: climb to the upper level to see the next jump
   target, relatively far below with ??? ammo.

   Continue along to an area with a left and right branch: the waypoint leads
   left, so instead go right to be surprised by 2 Imps. There's armor here
   (etc??)

   Go back to the left route, and (I recommend) activate In-Flight Mobility.
   Jump around the giant stalactite.

   Drop down to hear a demonic voice say "Kill Him".

   CHECKPOINT.

Mission 13: Fight: Wraith Fight 1

   You can start by sniping the Imps and Hell Knight, if you can see them
   from the cliff (you usually can). This can be a good time to get the Gauss
   Cannon's Precision Shot upgrade.

   Once you go down (irreversibly) into the arena, this fight is dominated by
   6 Pinkies and 2+ Hell Knights and a Cacodaemon.

   There's a Mega Health right after the CHECKPOINT for this, so it's quite a
   good place to start with Rich and Richer with Gauss Cannon / Siege Mode.

   There's a Quad-Damage Powerup here as well.

   Post Fight: there's a bunch of gear and a near the first Wraith's Soul.
   (This pattern will continue for the next two fights)

   There's are two parallel stairways leading up there: the one on the left
   has a Skull Switch that you should press.

   Go to the waypoint by first jumping to the high platform on the far side
   of the entrance (it has a BFG ammo on it, initially). From there, jump
   into the pale green mouth of a demon statue: it's lit with candles.

   Immediately past the mouth, turn right to a passage that only opens after
   the Skull Switch is pressed: this is SECRET 13.2. You'll find Gas and BFG
   Ammo.

   Continue down this secret passage, looking for bloodsmears and a lever on
   the left wall. As usual, interact with the level to open SECRET 13.5,
   CLASSIC MAP 13.1 "Doom - Pandemonium".

Mission 13: Fight: Wraith Fight 2

   Again, snipe a Hell Knight and 2 Imps from above, if you like.

   This fight starts with a Pinkie but I think there's only 1. There's tons
   of Hell Knights, Revenants, Imps, Hell Razers. And a string of about 4
   Cyber-Mancubi that tend to come at the end. The finale is a Cyber-Mancubi
   and Hell Baron that spawn at the same time.

   There's a Berserk Powerup here. Don't forget to use the chainsaw if you're
   low on ammo.

   Post Fight: on the way up to the waypoint (a Wraith's Soul), there's a
   bunch of supplies. On the left stairs going up, look for a big hole in the
   upper half of the stairs that's so big you can walk in under the stairs.
   This is SECRET 13.1, COLLECTIBLE 13.1: "Chaingun Model, Cosmoguy".

   Continue up to interact with the waypoint, then follow the waypoint to the
   next fight.

   You'll teleport to an area with molten rock. At you walk up this tunnel,
   keep an eye out for the third Skull Switch, on the right. Interact, then
   walk back toward the entrance to find an newly opened alcove, SECRET 13.4,
   containing Meta Health and BFG Ammo (don't forget to activate Rich get
   Richer before taking the health).

Mission 13: Fight: Wraith Fight 3

   Again, snipe a Hell Knight and an Imp before jumping down, if possible.

   This fight is a long sequence of Hell Knights and Pinkies and Imps. Toward
   the end a Cyber-Mancubi and finally 2 Hell Barons- you're easiest chance
   to get the Hold Still Challenge (use the BFG of course).

   Post Fight: gather supplies and interact. Follow the waypoint to the last
   fight, a boss fight.

Mission 13: Boss Fight: Spider Mastermind

   This is your big battle with demonic Olivia Pierce.

   Unlike the other boss fights, this one doesn't have a checkpoint in the
   middle.

   The first phase of the fight, is pretty standard:

     * Rocket Volley: a fast sequence of rockets. Keep moving in one
       direction to dodge.
     * Back-And-Forth Laser: a red laser that swipe one direction low (so you
       must jump over it) then it swipes back high, so you must crouch under
       it.

   When the demon gets to 50% health, she'll add:

     * Toxic Pond: Pillars sprout up that you must stand on, as the ground
       will be very damaging to stand up. The first time, that's all that
       happens. Subsequent times, Olivia will concentrate on the pillars, and
       when she jumps spikes will come out of the pillars, killing you if you
       are standing on them. Double jump in the air to avoid this fate.

   When she gets to around 10% health, she kind-of goes nuts, shooting many
   (fairly weak) lasers in all directions, and emitting these weird cubic
   missiles that do a lot of damage (dodge them).

   When she gets to 0% she'll stand up like she's going to attack or
   something, but she actually flops down and is Glory Killable. (There's no
   time limit, she won't recover from being staggered)

   You'll get COLLECTIBLE 13.2 "Spider Mastermind Model, Goldguy", along with
   6 Weapon Upgrade points.

   After that, watch a cut-scene and the credits.

            Appendix: Ultra-Nightmare Practice Sheet: Abbreviations

   You can download a practice sheet if you want to try to train for
   Ultra-Nightmare, and any player could use it to improve their skills.
   (TODO: as of 12-20-2018 I haven't yet actually made the practice sheet)

   Abbreviations for the Demon that killed you:

     * tp: The Possessed
     * uw: The Unwilling
     * ps: Possessed Soldier
     * ss: Possessed Security (aka Shielded Soldier)
     * hk: Hell Knight
     * imp: Imp
     * ls: Lost Soul
     * cd: Cacodaemon
     * mc: Mancubus (plural: Mancubi)
     * cm: Cyber-Mancubus
     * hb: Hell Baron
     * pnk: Pinky
     * sp: Spectre

   Modifiers:

     * immed: Immediate (w/i a few seconds) death from Checkpoint
     * oob: Out-of-the-Blue
     * ow: Overwhelmed

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