you need to have gotten the ruby and sapphire and given them to celio on one island. after that the man in front of cerulean cave should have moved and you have gained entrance to the cave. you need HM rock smash to get through the cave. mewtwo should be in there. good luck :D
Mewtwo.
Mewtwo!
Mewtwo is found in cerulean cave.
no, firered or leafgreen
Mewtwo, yes, if you have a FireRed or LeafGreen with Mewtwo.
Catch 'em all
No migrate him from firered or leafgreen to get him.
Yes it is in a cave.
He is at the end of cerulean cave.
you cant catch mewtwo in Pokemon emerald. to get it you must trade with either Pokemon firered or leafgreen.
Mewtwo? Plus you cannot get Mew in Leafgreen or Firered.
Face the Pokemon League again