There are no cheats in Pokemon unles you count the Action Replay but even that cannot get you new Pokemon, mew3 does not exist. To make it you would have to entirely change the game code.
you can't
No, you cannot.
There is no Mew 3.
no now shhh im trying to get to sleep
Mew three isn't a Pokemon just a fake made by a fan
no because there isn't a mew-three just mew and mew-two sorry
you only can get them with cheats (i realy hate that with all that events and cheats =[ )
Mewtwo? Plus you cannot get Mew in Leafgreen or Firered.
You can't get mew in firered or leafgreen.
There is no Mew in FireRed or LeafGreen.
in the celular cave after getting the three stones for island 1
beat elite 4 5 times then beat 30 different trainers isn't that good