Thornmantle Striker is a uncommon Creature — Elf Rogue card from Kaldheim (KHM), collector number 387. Current market price: $0.21, TCGplayer market prices via Scryfall.
When this creature enters, choose one — • Remove X counters from target permanent, where X is the number of Elves you control. • Target creature an opponent controls gets -X/-X until end of turn, where X is the number of Elves you control.