Arya's Prayer

When Arya's Prayer enters the battlefield, put a
-1/-1 counter on target creature.
At the beginning of each opponent's end step,
that player must sacrifice a creature with a -1/-1 counter on it. If that player cannot, put a -1/-1
counter on target creature that player controls.
Joffrey. Cersei. Walder Frey. Meryn Trant. Tywin Lannister. The Red Woman. Beric Dondarrion. Thoros
of Myr. Ilyn Payne. The Mountain. The Hound.