Shallow Graveyard

Shallow Graveyard enters the battlefield tapped.
{t}: Add {b}
{2}{b}, {t}: Exile the top card of target player's graveyard. If a creature card is exiled this way, create a 2/2 black Zombie creature token.
Otherwise, untap Shallow Graveyard. Activate this ability only any time you could cast a sorcery.