Ancient Cellarspawn is a rare Enchantment Creature — Horror card from Duskmourn: House of Horror Commander (DSC), collector number 47. Current market price: $6.76, TCGplayer market prices via Scryfall.
Each spell you cast that's a Demon, Horror, or Nightmare costs {1} less to cast. Whenever you cast a spell, if the amount of mana spent to cast it was less than its mana value, target opponent loses life equal to the difference.