I've been looking through my old emails, and I've found an email I got years ago, from a "Thomas Lei" about a Mew Glitch specific to Green. I can confirm (I did test via emulation when I got the email) that the Mew glitch does work...
I'll paste the details directly from the email.
There are two main glitchs:
1. Mew glitch
2. Lv.100 glitch
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To do the Mew glitch:
1. get 2 pokemons, water type***
2. have 13 items with you
3. get into battle
4. go to item
5. go to the 13th item(press down 12 times)
6. press select
7. press B
8. go to switch pokemon screen
9. press down(point to 2nd pokemon)
10.press A(the pokemon should turn to Mew)***
11.Now you can press B to cancel back to the battle screen and run away from battle OR kill the enemy to win the battle.
12.Heal your pokemon and put Mew into the PC then take it back out(it should fix the HP)###
13.Or simply trade it to another gameboy
***using other types your pokemon will turn into a "fossil" and the game freeze at step 10
***if you win the battle with this 'Mew', it will turn to lv.101
###it will mess up your item#1 so don't put bicycle at the first place in the item list(put potion ^^) and also some other things may not work probably.
---repeat the steps 1-10 will turn your Mew back to the original pokemon(the pokemon you turned into Mew will come back) and it will also fix all the problems you get when you hold the Mew(fix the item#1)
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To do the quick Lv100:
1. have a pokemon with at least 2 attacks(moves)
2. have 7 iteams
3. get into battle
4. go to item
5. go to the 7th item(press down 6 times)
6. press select
7. press B
8. choose attack
9. press down so it will point to your 2nd move(or 4th if you have 4 moves)
10.press A(that attack move will turn into another move and will have 0 pp ususally)***
11.Use other attacks and you MUST WIN THE BATTLE!!!
12.After you win the battle, you will gain 100 levels.
***at step 10, the move you choose to press A on will disappear(gone forever) so choose the most useless attack.
User is finally online...