From MTGSalvation:
Sewer Nemesis

Creature - Horror (R)
As Sewer Nemesis enters the battlefield, choose a player.
Sewer Nemesis's power and toughness are each equal to the number of cards in that player's graveyard.
Whenever the chosen player casts a spell, that player puts the top card of his or her library into his or her graveyard.
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Looking at the card, it has a dual-purpose: self-mill, and enemy-mill. I suppose it has potential as an alt wincon in Storm decks (outside of EtW), as well as LED-Based Dredge. Are there any other decks that this could slot into, and what would it replace?