Once you have defeated the Elite Four, you will earn access to the previously blocked Cerulean Cave found within none other than Cerulean City. Deep within Cerulean Cave, you will be able to find the Legendary Pokemon known as Mewtwo. Like other Legendary Pokemon Encounters found within the game, Mewtwo must first be defeated in battle before you will be allowed to capture it. In battle, Mewtwo will be at Level 70 and will have all of its Stats boosted at the beginning of said bout, knowing the moves of Psychic, Recover, Amnesia and Swift.
However, unlike other Legendary Pokemon Encounters, Mewtwo will be a little more difficult to capture once you have defeated it in battle. You see, Mewtwo has a special feature to bring up a barrier at given times when a player is trying to capture it. When this barrier is up, the effects of Berries are removed and the use of Poke Balls and other Berries is prevented. Only when this barrier is down can a player attempt to capture Mewtwo.
Need help Catching Mewtwo? Check out our How To Easily Catch Mewtwo Page!