Imminent Doom is a rare Enchantment card from Hour of Devastation (HOU), collector number 98. Current market price: $0.13 (foil $0.93), TCGplayer market prices via Scryfall.
This enchantment enters with a doom counter on it. Whenever you cast a spell with mana value equal to the number of doom counters on this enchantment, this enchantment deals that much damage to any target. Then put a doom counter on this enchantment.