Helm of Phenax

Whenever a creature you control deals combat damage to a player, you may exile up to X cards from that player's graveyard where X is the attacking creature's power. That player loses life equal to the number cards exiled this way.
{u}{b},{t}: Sacrifice a creature you control. Each opponent puts the top X cards of his or her library into his or her graveyard, where X is the sacrificed creature's toughness.