Fists of the Demigod is a common Enchantment — Aura card from Shadowmoor (SHM), collector number 187. Current market price: $0.26 (foil $8.00), TCGplayer market prices via Scryfall.
Enchant creature As long as enchanted creature is black, it gets +1/+1 and has wither. (It deals damage to creatures in the form of -1/-1 counters.) As long as enchanted creature is red, it gets +1/+1 and has first strike.