Wormfang Manta

This is an interesting card with loads of great combos: The worst of which is to simply give it phasing (come into play effects are ignored when something phases in, yet leave play effects trigger when it phases out). Instant infinite turns! But, if you don't want to loose all your friends, it goes great with copying cards (volrath's shapeshifter, etc.): copy it with something that's already in play, so the turn-skipping doesn't trigger, but then when the copy leaves play, you get an extra turn. You can also play something like a smokestack, tanglewire, or glacial chasm to help during the initial extra turn of you opponent.

P.S. when it comes into play and then is removed at the end of turn via Dawn of the Dead, both abilities trigger, so they cancel out.

Good Combo: First turn dark ritual + buried alive 3 mantas, second turn dark ritual + buried alive your last manta, 3rd turn cabal ritual (w/ threshold) + spreading plague (if they are playing blue creatures), 4th turn dawn of the dead, 5th turn bring out one wormfang manta and game over (you get turn after turn to hit them with the mantas). Complicated but fun!