Psychic / Poison
Mewthree has no effect to ground attacks.
Mewthree is able to mutate his arms to different shapes, changing its stats each 2 turns.
Mewtwo had a hunger for more power, so he teamed up with a professor who used to work for goivanni. The professor did yet another transformation on Mewtwo's DNA, causing him to turn into Mewthree. Since this experiment was done on him awake, he saw what the trick was. He can now change his arms by himself.