What if Harry had a twin brother who was in Slytherin? James is pretty much the darker version of Harry who doesn't fool around and doesn't hold back. James has a much darker view on life and balances on the line of good and evil, light and dark, Harry's opposite.

What if Peter wasn't the only one bitten by a spider? What if there was another student that got bit by a different spider and got the same abilities but with a little extra? And what if this person also became a hero like Peter but has a different outlook on fighting crime?