Muse of Sorrow

At the beginning of each end step, if you lost life this turn, exile the top card of your library.
{b}{b}: Return a card you own from exile to your graveyard. Each opponent loses X life and you gain X life where X is the number of cards exiled with Muse of Sorrow.
Whenever you cast a black spell, you may return Muse of Sorrow from your graveyard to your
hand.