3. Mister Sinister
Though the X-Men series has already had its share of characters who think that mutants are a supreme off-shoot of the human race, would another really hurt? Mister Sinister is a fascinating character who above almost all else wants to advance mutant evolution by any means necessary. What is perhaps most notable about the character, though, is the odd fascination he has with the Summers family, and the possibilities this might have for Days of Future Past; after all - and this is a
SPOILER ALERT - it is eventually revealed that Havok and Cyclops are brothers, and it's easy to see how this could have some possibilities for developing Sinister's villainous character. Internet speculation has already been rife that Sinister's appearance would almost certainly lead to the introduction of Apocalypse given how they've worked together in the comics, another tantalising possibility in of itself.