Appearing in "What If... Mr. Sinister Formed the X-Men?"
Featured Characters:
- X-Men (Sinister) (First appearance)
Supporting Characters:
Villains:
- Brotherhood of Mutants (First appearance)
- Magneto (First appearance)
- Quicksilver (First appearance)
- Scarlet Witch (First appearance)
- Toad (First appearance)
- Mastermind (First appearance)
Other Characters:
- X-Men (First appearance)
Locations:
Items:
Vehicles:
Synopsis for "What If... Mr. Sinister Formed the X-Men?"
- Synopsis not yet written