The Unbeatable Squirrel Girl is definitely worth a mention, especially considering Capcom are on record as saying she wouldn't be included in their Marvel vs Capcom series because she'd be game breaking as she, canonically, can't be beaten so incl... read more
To look for Marvel characters in general who have never been defeated, you must maybe look past heroes and villains. Look at supporting characters. But not those who are too frequent - even Aunt May got her share of defeat in some stories. read more
However, Batman is always prepared. He has thought of almost any contingency. Marvel characters would have a leg up on Batman, since he has never heard of them. Batman has never imagined a Hulk (or She-Hulk or Red Hulk) with shocking super-strength but no special vulnerability to magic or Kryptonite. Dr. read more
Dormammu. Source: Marvel Comics. Dormammu may be an extradimensional being, but he is by no means a god. A member of the demonic Faltine species, he has simply honed his magical abilities to insane levels - and if there's one thing - other than Kryptonite - that can defeat Superman, it's magic. read more