Change a character's moral alignment.

[LordUltimus]

Invert one characters morality. Maybe more than one, but not to the "Earth-3" extent. Make Spider-Man always been evil, Green Goblin always been good, etc., and extrapolate the chain of events and how characters they interact with are affected from there.

[gonnagiveittoya]

Nice try, Rick Remender

[Agent Z]

Instead of being a centuries old spree killer, Sabretooth is an ancient protector of the persecuted and destitute whose heroic exploit have been the stuff of legend but never actually proven. He is Wolverine's conscience and frequently tries to keep his friend on the straight and narrow path with varying results.

Mr Sinister is no longer a eugenicist and Nazi collaborator but a person who has dedicated his life to curing diseases.

[your_name_here]

Always liked Matt Muderdock in Spider-Gwen.

[Huntsman Spider]

Always liked Matt Muderdock in Spider-Gwen.

Yeah, that's a pretty cool inversion of Matt Murdock's character --- instead of him fighting the Kingpin and the Hand, he becomes a leader in the Hand and at first the Kingpin's lawyer and assassin, then the (acting) Kingpin himself once Fisk goes to prison, and whereas the Matt Murdock we know befriends his world's spider-powered hero, Murderdock seeks to exploit and corrupt his world's spider-powered hero as a way to give his own life some semblance of meaning, purpose, and/or justification.