Pugnacious Hammerskull is a rare Creature — Dinosaur card from The Lost Caverns of Ixalan Promos (PLCI), collector number 208p. Current market price: $2.29 (foil $0.90), TCGplayer market prices via Scryfall.
Whenever this creature attacks while you don't control another Dinosaur, put a stun counter on it. (If a permanent with a stun counter would become untapped, remove one from it instead.)