Walkthrough
Deep within Cerulean Cave, you will find the Legendary Pokemon Mewtwo. Mewtwo is one piece of the Kanto Legendary Mew Duo, being a pure Psychic Type Pokemon. It will be found at Level 70, knowing the moves Swift, Recover, Safeguard, and Psychic. Since Psychic and Swift are Mewtwo's only damage-causing attacks, Dark Type Pokemon and Steel Type Pokemon usually hold up well against Mewtwo. Even though Mewtwo is in a three way tie for strongest Wild Pokemon and thus makes it a good candidate to use the Master Ball on, it can still be captured using Ultra Balls.