Hmmmm. You need fake-life fun facts about each contestant. For example: Mewtwo was a high-school chemistry teacher who took to battling after winning a drunken bar brawl. He wants the money to build that lab he's always dreamed of.
My vote is Mewtwo though. He has the moveset to bring down all of the above barring shadow ball/sneak Giratina.
"I feel like I got hit with a Dracula, by King Kong." -BMO