One rumored card is pretty funny:
UU3
Instant
Counter target spell. Remove that spell from the game, then search that spell's controller's hand, library, and graveyard for all copies of that spell and remove them from the game. Then shuffle that player's library.
Note: wording is rough, but you get the idea.
Not sure if it's all hat playable outside of maybe a 2-of in T2, but it sure strikes me as funny, since so many people bitched about Extirpate being the ultimate card ever, etc.