Decomposition is a uncommon Enchantment — Aura card from Mirage (MIR), collector number 212. Current market price: $0.10, TCGplayer market prices via Scryfall.
Enchant black creature Enchanted creature has "Cumulative upkeep—Pay 1 life." (At the beginning of its controller's upkeep, that player puts an age counter on it, then sacrifices it unless they pay its upkeep cost for each age counter on it.) When enchanted creature dies, its controller loses 2 life.