While it is not known to evolve into or from any other Pokémon, it can Mega Evolve into two different forms: Mega Mewtwo X using Mewtwonite X and Mega Mewtwo Y using Mewtwonite Y. Mega Mewtwo X is Psychic / Fighting, has the Ability Steadfast, and its Attack, Defense, and Special Defense stats are increased. Mega Mewtwo Y has the Ability Insomnia and its Attack, Special Attack, Special Defense, and Speed stats are increased. However, its Defense stat is decreased.
It is among the most well-known Pokémon, being the star of the first movie and, in Generation I, the most powerful Pokémon in regards to its total base stats. It is a member of the Mew duo along with Mew.
Mewtwo is one of the first Pokémon created by science. The scientists who created it dreamed of creating the world's strongest Pokémon. It is unique in that it was the only clone to survive the cloning process before it destroyed the facility in which it was created. However, this has yet to be fully confirmed.
Mewtwo is a creature with a humanoid frame, but has some feline features. Mewtwo's body is grey with a long, purple tail. It has three circular pads on its fingers and opposable toes on the inside of its feet, like many real-world primates, as well as two others that face forward. It has purple eyes (that glow blue during some attacks) and two blunt horns.
One of Mewtwo's most notable features is the tube extending from the back of its skull to its spine. It is most likely a secondary spinal cord, or a system of nerves, allowing for an increased amount of blood and sensory transmission to the brain, heightening its psychic powers.
As Mega Mewtwo, it is smaller and is closer to Mew in size. Its head loses the tube and gains a large growth on the back that resembles its regular form's tail, a ring-shaped crest with two thin, pointed horns, and red eyes with faint scleras. Instead of a breastplate-shaped chest, it develops a long, bumpy ridge much like a sternum. Its forearms thicken, its fingers and toes become purple and smooth, and its middle toes become larger than the others. Its grey body takes on a purplish tinge, and the growth on its head is mostly purple.