Holy Ariel
how does one get that Mew? I've tried it but it never works for me
gonk
Sorry you had to wait so long for an answer.
1: The kid past the nugget bridge who has a slowpoke, you have to have never battled him, or else it's null.
2: You have to also never battled the gambler just south of the underground path doorway to the west of Lavendar town.
3: You have to have a pokemon that knows fly, one that can battle and not kill a lvl7 anything.
4: Save inside that particular undergound path, come out and instantly hit start. Fly to Cerulean city, as you do a "!" should pop up over the gambler like he wants to fight.
5: Game is glitched, but you want it to be, congrats.
6: Walk up to where the rich kid is, but don't walk straight up to him for a battle, make him walk at least one square to you.
7: Now you're really in a battle, just beat him and your start button will work again [It won't work until you do this because thanks to the gambler the glitch is, your game thinks you're in a battle.]
8: Fly back to Lavendar town and walk onto route 8 [The one the gambler is on] Start menu will pop up. Exit the menu and a lvl7 Mew will attack. Not sure if it can be done multiple times. But you could try.