In this dungeon you'll find Pokémon of all types over Level 50. In the northwest section of the cavern, you'll meet the strongest Pokémon of them all, Mewtwo.

Mewtwo L70- Swift, Psychic, Barrier, Recover Just use the Master Ball you saved. It'll be hard to catch Mewtwo without it. If you don't have one, just put it to sleep numerous times, weaken it so it has a tiny bit of HP left, and keep using your Ultra Balls.