Thoughts on a alternate Harry Potter ending where Harry goes to the Forbidden Forest to die, but is swayed by Voldermort into joining the dark side. He goes back to the castle, Hermione and Ron embrace him as they think he conquered Riddle but then bam, Avada Kedavra outta nowhere? Possibilities would be endless, you could have Harry return to the good side eventually, or even Voldermort returning when he sees the destruction Potter had caused. Either one could also kill the other to further their ambition (would work better if Harry betrayed Voldermort tbh), Neville could also step into the chosen one role.