Pray for Swift Death

When Pray for Swift Death enters the battlefield,
put a corpse counter on it. Durning your upkeep,
put an additional corpse counter on Pray for
Swift Death.
At the beginning of each opponents end step,
that player sacrifices a creature for each
counter on Pray for Swift death, if able.
That player may pay {5}; if they do, instead,
creatures that player controls have -1/-1 until the beginning of their next turn.