Mewtwo is imperfect. He was created in an attempt to clone the ancestral Pokemon, Mew. Mew's origins are not known, what is known is that within its DNA lies the building blocks to all Pokemon. Mew has the appearance of an embryo and it seemingly never ages. Mewtwo did not receive this genetic perk. At first hatching it appeared to be a perfect success, though the clone started growing. It eventually grew too strong to be kept under restraint, in its escape destroyed the research facility it was created in. In this purge it freed other undeveloped Mew clones. The cloned sludge, left without a body or identity, yet still with the incomplete building blocks of all Pokemon wander aimless seeking others of their kin. They are known as Ditto and have become a plague on wild Pokemon, killing an absorbing their prey and filling their broken DNA with strains from the world's Pokemon species.

Design wise, I really wanted to bring the theme of birth and life into Mew and by extension, Mewtwo. They both have an umbilical cord ending in a placental brain wrapping around their tail. Mewtwo shares traits with many other Pokemon species as Mew was never supposed to grow, so it took on traits of various Pokemon from its genetic party bus of DNA.