how do u make mewtwo the most powerful pokemon?

Answer 1

Raise Mewtwo to level 100 and feed him all the proteins, carbos etc until the game will tell you it will have no effect. Then Mewtwo will be the most powerful Pokemon in your party...however, this can apply to other legendaries too, even the strongest Pokemon have weaknesses. For example, since Mewtwo is a psychic type, he's weak aganist dark type attacks.

Answer 2

Make him lv. 100 and feed the stat ups( like protein or iron from the celedon city shopping mall) and raise its Sp. attack and defense stats.
Give it moves like:
Thunder
Flamethrower
Ice Beam
Psychic