Exemplar of Strength is a uncommon Creature — Human Warrior card from Amonkhet (AKH), collector number 165. Current market price: $0.20 (foil $0.19), TCGplayer market prices via Scryfall.
When this creature enters, put three -1/-1 counters on target creature you control. Whenever this creature attacks, remove a -1/-1 counter from it. If you do, you gain 1 life.