Nils, Discipline Enforcer is a rare Legendary Creature — Human Cleric card from Commander 2021 (C21), collector number 20. Current market price: $2.13, TCGplayer market prices via Scryfall.
At the beginning of your end step, for each player, put a +1/+1 counter on up to one target creature that player controls. Each creature with one or more counters on it can't attack you or planeswalkers you control unless its controller pays {X}, where X is the number of counters on that creature.