Re: Apocalypse (from x men)
He's not a powerful as Phoenix (though that may not count), but he's strong enough to handle several heroes at once and even beat the Hulk one on one. His power is the ability to manipulate his molecules to allow him to change into almost anything. He was augmented using Celestial tech. In a alternate timeline, he conquered most of the Earth with the X-Men working as freedom fighters. I don't know if he's the most powerful, but he's high up there. The only mutant I can think of that might be higher in scale is the Scarlet Witch.
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