X-Men: 10 Characters That Must Appear In The New Mutants Movie
4. Magik

In New Mutants continuity, Illyana Nikolievna Rasputina, younger sister of the X-Man Colossus, was only six years old when she was kidnapped by demons, taken to a pocket dimension called Limbo and trained in the sorcerous arts, only to be dragged back to Earth seven years later by her reckoning, but instantly for everyone else: a thirteen year old girl raised by devils, with an evil ‘Darkchilde’ side trying to take over, and all kinds of other messed up cr*p to deal with.
Her mutant power is the ability to create ‘stepping disks’: teleportational portals that can transport herself and an undetermined number of other people/things an almost unlimited distance. Part of the rationale for teleportation in the Marvel Universe is that the teleporter uses an alternate dimension in space/time as a stepping stone, bouncing from A to X to B: well, Magik’s power does likewise, just with the constant possibility of being trapped in X halfway through the jump.
If the introduction of black magic and demons is a narrative step too far, then an adaptation of the character could simply have Illyana first manifest her mutant ability at a pre-teen age and vanish, only to reappear days later as a sword-wielding psychologically scarred badass twice the age she’d been when she left.
Instead of a hell dimension, Limbo can be recast as Monster Island. Somehow, little Illyana manages to survive there for years, but became half a monster in doing so. The story of Magik’s kidnapping, her mysterious aging to adolescence and her savage, uncontrollable shadow self is the gimmick here.
And yes, for those genrehawks amongst you: Magik’s backstory is the X-Men storyline that Mutant Enemy stole wholesale for Connor, Angel’s half-demon son in season three of the Buffy The Vampire Slayer spin-off… so turnabout being fair play, stealing Connor’s backstory for a movie version of Magik seems perfectly acceptable to me.