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 widely considered unique, because only one was genetically created. However, this has yet to be fully confirmed.

Mewtwo is a creature with a humanoid posture, but has a few feline features. Mewtwo's body is grayish-purple with a purple underside and a long, purple tail. Mewtwo has three circular digits on each appendage. It has purple eyes (sometimes blue when attacking) and two short ears.

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.