Mewtwo is a Psychic-type Genetic Legendary Pokémon.
While does not evolved into or from the any other Pokémon, it can Mega Evolve into two different forms: Mega Mewtwo X using Mewtwonite X and Mega Mewtwo Y using Mewtwonite Y.
It is a member of the Mew duo along with Mew.
Mewtwo is a Pokémon created by science. It is a bipedal, humanoid creature with some feline features. It is primarily gray with a long, purple tail. On top of its head are two short, blunt horns, and it has purple eyes. A tube extends from the back of its skull to the top of its spine, bypassing its neck. It has a defined chest and shoulders, which resemble a breastplate. The three digits on each hand and foot have spherical tips. Its tail is thick at the base, but thins before ending in a small bulb.
Mega Mewtwo X is larger and bulkier than its normal state. The horns on its head are longer, extending from V-shaped ridges on its forehead, pointed, and curved upward. It retains the tube behind its neck, but its eyes are now light blue, and it has large, purple growths over its shoulders. Its torso is smooth and small compared to its long, bulky limbs, and a Y-shaped line connects the collar and underbelly. Its forearms and thighs each have two raised ridges, and its digits are now longer and thinner. The tail is slightly shorter and stiffer than before and has a curled tip.
In comparison, Mega Mewtwo Y is smaller and lighter, losing its long tail and the tube behind its neck. However, it grows a long, purple appendage with a curled tip from the back of its head that is similar to its previous form's tail. On its head it has two pointed, backward-curving spikes and a half-ring structure connecting the base of each, with empty space inside. Its eyes are now red and slightly larger. The digits on its hands and feet are now purple and more bulbous, and the middle toe is longer than the others. A bumpy ridge similar to a sternum replaces the breastplate structure on its chest, but this form is still largely smoother than the other two.
Mewtwo was created after years of horrific gene splicing and DNA engineering experiments based on Mew. It is said to have the most savage heart among all Pokémon, lack compassion, and strike fear into its enemy with cold, glowing eyes. Because it was engineered to be the ultimate in battle, it can only think of defeating its foes. In the first movie, Mewtwo exemplified these vicious characteristics and was shown to be capable of levitation, telepathy, and mind control. However, it was later shown to be caring, protective, and even altruistic. Another Mewtwo in the anime shared its aversion to contact with others, but was much less belligerent. Mewtwo conserves energy by remaining motionless to unleash its full power in battle. It is also capable of materializing psychic waves in the form of its signature move, Psystrike. Though rarely seen in the wild, it is said to be resting in a dark cave somewhere.
According to the scientific logs found in the Pokémon Mansion of Cinnabar Island, Mewtwo was born of a pregnant Mew, found deep in the jungles of Guyana, whose embryo had been tampered with to alter its DNA. It was held and studied in the mansion where a scientist performed horrific gene-splicing experiments that made it vicious and extremely powerful. It eventually broke free of the Mansion, destroying it in the process, and fled. It can be encountered in Cerulean Cave, accessible only after a Trainer has proven his or her skill at the Indigo Plateau.