Sewer Nemesis is a rare Creature — Horror card from The List (PLST), collector number CM2-75. Current market price: $1.03, TCGplayer market prices via Scryfall.
As this creature enters, choose a player. Sewer Nemesis's power and toughness are each equal to the number of cards in the chosen player's graveyard. Whenever the chosen player casts a spell, that player mills a card.