Unstable Mutation is a uncommon Enchantment — Aura card from Ultimate Masters (UMA), collector number 80. Current market price: $0.07 (foil $0.27), TCGplayer market prices via Scryfall.
Enchant creature Enchanted creature gets +3/+3. At the beginning of the upkeep of enchanted creature's controller, put a -1/-1 counter on that creature.