My favorite mutant? Well, he appears in Captain America Annual #4, pulled straight from the way-out, wacky, and weird mind of Jack "The King" Kirby. And no, my fave mutant is not Magneto...
All panels from Captain America Annual #4 (1977), written and pencilled by Jack Kirby, inked by John Tartaglione and John Verpoorten, coloring by George Roussos, lettering by Jim Novak
...It's this guy:
The heck with another Wolverine or X-Teens spin-off...it's high time to give Tiny Mutant Who Lives In a Wristwatch Guy his own series. Bring him back as the new Professor X. Bring him back as the new X-pionage Secret Weapon. Heck, bring him back as The Beast's fashion consultant, I don't care. Just bring him back.
Jack Kirby's world: holy cow, it's amazing. I'm not certain I wanna live in The World of Kirby, but it's a heckuva place to spend a holiday, isn't it? Or, to paraphrase J. B. S. Haldane: "Not only is Jack Kirby's universe stranger than we imagine, it is stranger than we can imagine."