O'Man, Summoner of Dread

While O'Man is on the battlefield or in the
command zone, at the begining of your turn, you
may send a creature card of your choice from
your library to your graveyard, then shuffle.
{u}{u}{b}{b}: You may cast creatures from your graveyard this turn.
If O'Man, Summoner of Dread is sent to the graveyard from anywhere, sacrifice a creature.
If you do, put O'Man, Summoner of Dread onto
the battlefield and you lose 7 life.