The Harry Potter Battle Royale: A hundred Harry's from different fanfics and canon, are pulled into an interdimensional arena.
They may bring their wand and ONE other thing (could be person, and artifact, etc.) The main characters from all their stories are invited to watch the battle of the dimensions. (No godlike Harry's. it'll break the game).
The last Harry standing is the winner, and gets to ask a boon from fate.