When the battle was over, after all the blood it shed in the search for truth and freedom, Mewtwo made a solemn vow never to kill again and sealed itself within the Unknown Dungeon. Once the most powerful pokemon in Kanto if not the world, today it knows one damaging technique, a blade of psychic energy carefully controlled only to wound, which some say is reversed from a normal Psycho Cut's position.
Mewtwo's other techniques are strange ones, more mourning than attack or defense. At times it sends visions of the distant past to the opponent, doing nothing but strengthening its own resolve to survive. At other times, it tries to commune with its opponent, typically a vicious and powerful pokemon or a megalomaniac trainer, but does nothing but swap stat boosts and penalties regardless of need. Once it was found lying unconscious deep in the cave, beaten by a newborn Murkrow it was unable to damage in any way.
This is all established fact, while most wild pokemon of similar strength are still clouded in legend, for Mewtwo refuses to kill those it vanquishes in combat. At times, it even goes so far as the cave's entrance and gives directions back to the Pokemon Center; the defeated would typically prefer death to such a humbling.
Along with the usual crackpots, great trainers, and wild pokemon, at times Mewtwo is confronted by the loved ones of those it had killed in its rampage. It does not raise a tripod hand to its victims, allowing them instead to beat them to within an inch of its life, but it always recovers. It finds penance in this self-flagellation, but it is nothing of the sort. Perhaps someday, Mewtwo will finally begin to atone.
