O'man, summoner of dread

While this card is on the field or in the command zone, you can send a creature from your library to the graveyard.
While this card is on the battlefield, you can pay {p/b}{p/b}{p/u}{p/u} to cast undead creatures from your graveyard.
If this card is sent to the graveyard, sacrifice a creature, reanimate it then take damage equal to
its converted mana cost