Carnival Hellsteed is a rare Creature — Nightmare Horse card from Return to Ravnica (RTR), collector number 147. Current market price: $0.21 (foil $0.26), TCGplayer market prices via Scryfall.
First strike, haste Unleash (You may have this creature enter with a +1/+1 counter on it. It can't block as long as it has a +1/+1 counter on it.)