Beirt, the Soul Debtor

Whenever a creature dies, you may pay {w/b}. If you do, exile it.
{3}{w}{b}, {t}: Return target creature exiled with Beirt, the Soul Debtor to the battlefield under your control. That creature is a white Spirit or black Demon in addition to its other colours and types. You lose life equal to half of its coverted mana cost, rounded down.