4. Mister Sinister
Mister Sinister is a truly superb character. A powerful villain, he has been a staple figure in the creation and manipulation of several key characters in the X-Men comic books (including a few on this list) and an appearance from him in the live action adaptations would be most welcome. He possesses superhuman strength and durability, telepathy and telekinesis, a regenerative healing factor and the ability to manipulate matter at a molecular level, as well as being a formidable hand-t0-hand combatant. With Apocalypse rumoured to be a future on-screen X-Men villain, it would be no surprise to see Mister Sinister an associate of his appearing alongside him. On that note...