Valnus, Larceny of the Polis

When Valnus, Larceny of the Polis enters the battlefield, choose another player.
As long as you control Valnus, the chosen player can't use his or her graveyard's contents for spells and abilities. Treat the contents of the chosen player's graveyard as though they were in your graveyard for spells and abilities. Cards and permanents are still put into that player's graveyard as normal.