8. The Shadow King
Like Mister Sinister, this role would be well-suited to Peter Dinklage, given that The Shadow Form doesn't have a physical body on Earth, and instead inhabits human "hosts" when he comes to visit and cause wanton destruction. Though we're not sure if Dinklage would be a good fit for the King's human form - given that this would likely be CGI-free and therefore potentially get into daft territory - he could no doubt lend a superb vocal performance, while the various human forms he assumes can be pawned off to other actors. It would be easy to tie The Shadow King into the Sentinels storyline, and given that he's been a long-time adversary of Charles Xavier in the comics, there would be a certain natural antagonism that fans of the comic books would go crazy for. If Singer would feel the need to explore the non-human aspects of the character, though - specifically the astral plane on which he otherwise resides - then things could get a little dicey.