Mario uses the trick for nigh infinite lives off a koopa shell, mewtwo won't stand a chance.
Mario
Mewtwo
I'm curious as to which version of Mario we're using, or are we giving him everything he's ever had in all the official spin offs. I'm fairly certain that the end boss of The Thousand Year Old Door is more powerful than Mewtwo, and Mario beat her. So you'd think that the Mario from it, or a general Mario with that Marios power, could beat Mewtwo.
Absolutely no competition. Mewtwo would slaughter Mario with a single thought. Literally.