Shadow Mega Mewtwo X is the strongest form of Mewtwo. He is Dark, Fighting and Psychic type. He is extremely powerful.
He looks like Mewtwo, except he has some muscles, and a bulkier body. He also has a few other additions. He is also dark colored.
Shadow Mega Mewtwo X is smart and wise. He is quite powerful. His personality is just like Mewtwo's. His eyes may also turn purple and glow. When this happens, Shadow Mega Mewtwo X turns evil. This does not happen for Me, and only for Mewtwo.
In the Locked Rooms
Mega Mewtwo X transformed into it when he was attempting to destory the Dark Star, as dark energy flowed into him.