Brineborn Cutthroat is a uncommon Creature — Merfolk Pirate card from Jumpstart 2022 (J22), collector number 278. Current market price: $0.24, TCGplayer market prices via Scryfall.
Flash (You may cast this spell any time you could cast an instant.) Whenever you cast a spell during an opponent's turn, put a +1/+1 counter on this creature.