3. Arcade
If Bryan Singer opts to use Arcade in Days of Future Past, then expect an interpretation that doesn't resemble the above all that much, and as such, Dinklage's casting might actually work. Arcade is a classic comic book villain; a mad scientist who uses his enormous wealth to construct contrived death traps to execute people for money, these traps usually resembling either an arcade machine or the circus. As with other antagonists on this list, he would probably be too campy in his current form, so expect the zanier aspects to be jettisoned, but if streamlined, Arcade could make for an imposing and savagely intelligent foil to the X-Men. Given how other entries have altered characters to suit the tone of the movies, this shouldn't be a problem in the slightest.