Power manifested in a creature so vile, it makes you tremble to think how humans, through DNA splicing and engineering, were able to create such a monstrosity. Mewtwo is more than a pokemon, it's an example of the kind of power us humans would like to possess; that's why everyone connects with it and makes him the victor against any other creature. There's Deoxys, Lugia, Ho-oh, Groudon and Kyogre, there's Palkia, Dialga and even Darkrai but nothing really compares to the power and willingness to cause harm that Mewtwo possesses. It would be interesting though to face off Mewtwo against Arceus and witness Mewtwo obliterate Arceus from the inside out with the power of his mind done with but a single blink of his eyes!
Mewtwo concludes, "I wasn't born a Pokémon, I was created; and my creators have used and betrayed me! So, I stand alone!" Then goes on to destroy the entire facility along with everyone in it!