Sewer Nemesis

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.

Commander Legends: Battle for Baldur's Gate

As Sewer Nemesis enters the battlefield, 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.

The List

Commander Anthology Volume II

As Sewer Nemesis enters the battlefield, 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 puts the top card of their library into their graveyard.

Commander 2011

As Sewer Nemesis enters the battlefield, 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 puts the top card of his or her library into his or her graveyard.

If the chosen player leaves the game, Sewer Nemesis's power and toughness each become 0. Unless another effect is raising its toughness above 0, it will be put into its owner's graveyard as a state-based action.