Source: comicvine.gamespot.com

1. Matthew Malloy

Unclassifiable

Who? Yeah, I know, it's not super satisfying to see someone in the Number One slot and not recognize them, but Matthew Malloy is canonically Marvel's most powerful Mutant.

When discovered, he was said to be the most powerful Mutant signature Cerebro ever recorded. Matt had a hard beginning. His wife was killed in front of him by a Skrull invader during the Secret Invasion. After he went to live with his sister, his powers activated, and he annihilated everything around him. SHIELD dispatched a drone to see what was up with him, but he started getting agitated. Cyclops and Magik arrived to recruit him into the X-Men, but a SHIELD airstrike killed all three of them.

Matt reconstituted himself at the Jean Grey School, where he reacted to Emma Frost's attempts to calm him down by killing her. To stop his rampage, Tempus used her abilities to travel back in time. She prevented Matthew's parents from meeting, and erased him from existence. And that's what puts Matthew at Number One. Not his energy output that can level countries, not his reality and space-warping immortality, not his infinite telepathy, but the fact that he's the only Mutant so powerful that he couldn't be allowed to exist.

Power Level: Too powerful.

And there you have it, the ten most powerful Mutants, according to Marvel's own classification system. Like it, don't like it, have an issue with it? Let me know.