Mewtwo was the second in the M-2 line, the first to be recreated from Mew's genes, but also having features added as they thought they were needed. It's predecessor, M-2 Specimen A, was the attempt to recreate Mew entirely from the fractured genetic strand, and died upon creation. However, B's increased resilience and the filling in of the holes resulted in his birth and subsequent life.

Because B was the first to live, he was put through horrific tortures in order to learn more about them, tortures that, to this day he cannot forget. He was branded with his letter on the bottom of his left foot, and it cannot be removed, although he is able to hide it with his power. B began to hate the humans, but more then that he began to hate himself for living. From the scientists glowing speech about Mew and its possibilities and how it was the key to so many mysteries, B became enamored with the very concept of Mew, idolizing it as what he originally should have been.

Prof. Denka's restraining collars kept B's powers under check, but there was only so much they could learn from him. Dr. Kagakusha was already pressing for a new study, a new specimen, and they were forced to be rid of B. He was shot and thrown into the Unknown Dungeon, expected to die and give them no more trouble.

B's ability to recover allowed him to continue to live, although he moved as far away from his home of nightmares and as deep into the dungeon as he dared. He managed to elude the guardians in the caverns as well, and finally found somewhere where he could be alone. He blamed himself for being thrown out and replaced, and again ferverently wished that he could be his idol, Mew. This is where he christened himself with his new name, Mewtwo, and abandoned the title "M-2 Specimen B" forever.

After living down in the darkness for years, he finally came upon a startling discovery. Lying in the dark near the entrance, where they occasionally threw out other dead specimens that Mewtwo could feed upon when there wasn't enough food, he found a human boy. Confused, he carried him back to his lonely home on his island, and waited. The boy slowly recovered, and didn't seem to know anything. Mewtwo, never having had someone speak to him directly, was surprised to hear the boy address him as if there was nothing wrong with him. He didn't know what his name was, but he knew it started with D, and the two eventually decided that Drak would be a good enough name for him.

The two lived together for a long time, learning from one another and strengthening a psychic bond between them that could not be matched. They were the only thing they had in the world and they vowed to never be apart. Their friendship was equal in all ways, and Mewtwo helped Drak develop some kind of rudimentary psychic power through practice, although nothing special.

They lived together for what seemed like years, until their happy existence was broken by an intruder. The intruder managed to weaken Mewtwo, and, despite Drak's protests, imprison the Pokémon in a Pokéball, a process that Drak had never seen before. With that, the abnormally tall man dropped the ball into Drak's hand, with one cryptic sentence before he left.

"If this is what was taking care of you, then it is your turn to take care of it."

And then he was gone, before Drak could even find out anything about him. After that, Mewtwo seemed to technically "belong" to Drak, although they both hated it, and Drak was forced to leave the dark cave, not sure of how to free his friend. Once on the outside, he knew that he could no longer stay in the darkness, and after finding out more about Pokémon and a world he never knew about, they managed to find a job in a tournament for money. This is when they met Ella E, and Mewtwo's life slowly fell apart as Drak's attention moved from Mewtwo to Ella E, and Mewtwo began to feel left out. Not to mention that he didn't even belong to Drak anymore, he technically belonged to Ella E's, and he hated that even more. Around this point, he met Eclipse, a Gencey.

Eclipse gave Mewtwo a mother figure that he had never known through the power of the Mother's Lullaby, and finding someone else to focus his attention on, he became almost obsessed with Eclipse, listening to her advice in almost everything he did. He truly believed she was his mother, and he believed everything he told her. Still, doubts remained for him whether she was truly his mother, but these were somewhat laid to rest when they were able to perform a joint move, the Blood Vortex.

Mewtwo and Drak stayed at Ella E's house for only a short while until Drak was kidnapped. Mewtwo was distraught, trying to hide his loneliness behind his mother, and now his only real friend was gone. Mewtwo was forced to recall his past that he had tried to forget, and to remember where they might have taken his only true companion. With Eclipse and the others, he set out to rescue Drak, but found himself in deeper then he had ever thought...

Mewtwo is in Howl of a Growlithe and Koinonayami and a few other fics.

He has been mentioned in a few fics.