Six-y Beast is a uncommon Creature — Beast card from Unhinged (UNH), collector number 89. Current market price: $0.25 (foil $2.00), TCGplayer market prices via Scryfall.
As this creature enters, you secretly put six or fewer +1/+1 counters on it, then an opponent guesses the number of counters. If that player guesses right, sacrifice this creature after it enters.