Carnival Hellsteed is a rare Creature — Nightmare Horse card from RNA Guild Kit (GK2), collector number 62. Current market price: $0.16, 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.)