Desecration Demon

Creature — Demon

Flying

At the beginning of each combat, any opponent may sacrifice a creature of their choice. If a player does, tap this creature and put a +1/+1 counter on it.

Players won't know which player, planeswalker, or battle Desecration Demon will attack, if any, when deciding whether to sacrifice a creature.
Each opponent in turn order may choose to sacrifice a creature, even if an opponent already chose to sacrifice a creature that combat. Desecration Demon will have a maximum of one +1/+1 counter put on it each combat, no matter how many creatures were sacrificed.