Why does everyone always go for direct attacks?
Mine would be something along with an Evil Eye (or Entropy Curse from Dresden files) combined with a part that makes the opponent the target of a Xanatos' Gambit.
Result: Accidents happen to him with constantly increasing frequence and everything, literally everything he can do or does, somehow ends up benefitting me directly or indirectly.
Challenge your enemy, hit him with this, give up the fight and then watch the last few hours of his life as a trouble magnet while reaping the rewards from any and all actions he takes, including inaction