Shrine to Erebos

At the beginning of your upkeep, sacrifice Shrine of Erebos unless you sacrifice a creature.
{t}: Add {b} to your mana pool.
{x}{b}, {t}: Target player loses X life. If there are four or more creature cards in your graveyard, that player loses X times two life instead.
True believers come to this place to give up their life for the god of death.