After you clear a floor the first time, up on any return visits, there's a small chance that the floor will be...irregular. Examples of irregularities include no Shadows and lots of treasure (but the Reaper spawns super fast), the maps disappearing and visibility being reduced, or another in which every Shadow that spawns is gold.
Clear the areas between two sub-bosses, then grind til all the Shadows in those areas run from you. After that, rush from the teleporter on one floor to the other until you get an all-gold floor.
Formerly a panda, formerly a carnivore. Now just a guy without a catch phrase. https://imgtc.com/i/uVS7l1o.jpg