Cheapest priced copy (Secrets of Strixhaven Commander): $0.59 at Card Kingdom, near mint, their price list as of .
Nils, Discipline Enforcer 
Legendary Creature — Human Cleric · 2/2 · Rare · Commander 2021 · #20
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.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
4 printings · $0.59 to $3.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander 2021 | 20 | Rare | $0.69 | — |
| Commander 2021 | 347 | Rare | $3.49 | — |
| The List | C21-20 | Rare | — | — |
| Secrets of Strixhaven Commander | 158 | Rare | $0.59 | — |
3 rulings from Wizards of the Coast
- 16 April 2021All counters on a creature are considered when determining the value of X, not only +1/+1 counters.
- 16 April 2021For each player, choosing a target creature that player controls is optional.
- 16 April 2021Your opponents can choose not to pay to attack with a creature with one or more counters on it that attacks "if able." If there's no other player or planeswalker to attack, the creature simply doesn't attack.