Mewtwo is a Pokémon created by science. It is a bipedal, humanoid Pokémon 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 and extend from V-shaped ridges on its forehead. Additionally, the horns are now pointed and curve upward. It now has two tubes behind its neck, its eyes are 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. Its muscles are augmented with psychic power, giving it a grip strength of one ton and the ability to sprint 100 meters in two seconds. When using moves in battle, it is shown to be able to stretch its arms and legs.
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 to the base of each and crossing over the top of its head. 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. Despite its size, it has phenomenal mental power and is capable of smashing buildings with a mere thought.
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, where it was shown to be capable of levitation, telepathy, and mind control, Mewtwo exemplified these vicious characteristics. 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 in order 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 from 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.
In File 4: Charizard, after finding out about its existence from Blue, Red entered Cerulean Cave to add Mewtwo's data to the Pokédex. In a fierce battle that wiped out almost all of Red's Pokémon, Mewtwo was finally defeated by Red's Charizard after it Mega Evolved into Mega Charizard X. Red then proceeded to catch Mewtwo, making his collection of the 150 known Pokémon complete.
A Mewtwo appeared as the focus of The Discovery, where Green and Trace raced to try and catch it, only to discover that Elaine had done so minutes beforehand. Elaine used it in a battle against Green and her MegaBlastoise, where it won easily.
Pokémon Pinball: Mewtwo appears in its own bonus stage, where the player must attempt to hit it 25 times within the two-minute time limit to win. Playing this stage repeatedly is the fastest way to build a high score, due to the extremely high point output of 50,000,000 points per hit earned by hitting Mewtwo.
The island country of Niue released a one-dollar coin featuring Mewtwo as part of a commemorative promotion for the Pokémon franchise, with Mewtwo on the reverse side and the nation's crest on the obverse.
Mewtwo was originally depicted as the only member of its species, being a clone of Mew. In the anime and manga, however, it is implied that multiple Mewtwo have been created.
Mega Mewtwo X's Attack increase is the largest single stat increase of all Mega Evolutions, at 80 points.
Mega Mewtwo Y has the highest base Special Attack of all Pokémon and the highest single base stat of all Psychic-type Pokémon.
With a mild nature, perfect IVs, and optimized EVs, a Level 100 Mega Mewtwo Y's stats sum to 2,038: the highest sum of any Pokémon.
Mewtwo and Charizard are currently the only Pokémon with two Mega Evolutions.
In Pokémon GO, Shadow Mewtwo is the only Shadow Pokémon that has a different aura from the other Shadow Pokémon; instead of purple fire, it is surrounded by an aura resembling its Psychic power. It does not have a unique appearance when purified, however.
In Pokémon Gold, Silver, and Crystal, wild Mewtwo are programmed to always be holding a Berserk Gene, but since Mewtwo can't be found in the wild in those games, the item cannot be obtained that way. Even if it could be found in the wild, the item would be consumed immediately, so it still wouldn't be obtainable from Mewtwo.