Momentum Rumbler is a uncommon Creature — Dinosaur card from Ikoria: Lair of Behemoths (IKO), collector number 126. Current market price: $0.19 (foil $0.27), TCGplayer market prices via Scryfall.
Whenever this creature attacks, if it doesn't have first strike, put a first strike counter on it. Whenever this creature attacks, if it has first strike, it gains double strike until end of turn.