I mean if we're talking storylines then Thraxios (the wizard who split apart and then reforged the InVerse) is not currently accounted for, having travelled to another universe using high-level magic (though the inhabitants of the InVerse don't know, they think he just disappeared). He'd definitely work for a villain, having literally caused universe-scale chaos and death just to test the limits of his magic, but don't ask me how he'd lose. He's above the level of dudes like Thanos (with Infinity Stones) and Galactus. Sooooo maybe not.