This here is Ace. He's part of Bowser's army, but he is secretly working AGAINST him and not for him. He wants the people of the Mushroom Kingdom to stop having to worry about his evil actions and not live in fear of him, so he pretends to serve under him to eventually find a perfect opportunity to thwart his plans.

Though, Ace has his own problems he has to also deal with. There's an orb piece that he owns that is part of a much bigger artifact, and if he loses said thing, a lot of bad things will begin to happen to him. If lost or falls into the wrong hands at all. Bad luck will continue to compound upon him until... Game Over.