Mewtwo

Mewtwo is a Legendary Pokémon, and one of the most feared creatures to exist in Kanto.

History
Mewtwo has quite the tragic backstory. It was artificially created by scientists, who were possibly linked to Team Rocket. The scientists used Mew's genetic material to create Mewtwo; it later turned on those same scientists. Judging by the reactions of Victor, Cobalt, and the Contest audience in Cerulean City, Mewtwo then went on a rampage that was so terrifying and destructive that Kanto's citizens are even afraid to speak its name out loud.

Its current location and status are unknown.

Description
Mewtwo is an intimidating creature that could be described as a bipedal, humanoid cross between a cat and an embryo. Its fur or skin is purple, and it has terrifying psychic powers that may be without limit.

Trivia

 * Mewtwo may be residing within Cerulean Cave.
 * Scramble channeled Mewtwo's Psycho Cut during the Cerulean City Contest, terrifying the living daylights out of almost everyone in attendance (except Rose), only adding to her reputation of being a demon in disguise.
 * The citizens of Kanto refusing to call Mewtwo by name, either out of terror, superstition, or respect, is similar to the treatment of Voldemort's name in the Harry Potter Series (where he is called He-Who-Must-Not-Be-Named).