General Gelid

If Milton had a weakness, it was the cold. Anything below room temperature would make him start to shiver uncontrollably and if it got down to freezing, he'd begin vomiting.

Milton knew his comic books though. Every hero had a fatal flaw, his own personal kryptonite, so to speak. Milton's susceptibility to the cold would be his. Obviously, his mortal enemy, his arch-nemesis, would be a villain who used cold as a weapon. Maybe his name would be General Gelid or something like that.

Sadly for Milton, while he might have a weakness, he didn't have any discernible super powers.