Mary O'Kill is a rare Legendary Creature — Human Villain card from The List (Unfinity Foil Edition) (ULST), collector number 50. Current market price: — (foil $0.18), TCGplayer market prices via Scryfall.
{1}{B/R}: Switch a Killbot or Mary O'Kill in your hand with one on the battlefield. (If a creature is tapped, the switched creature is tapped. The same is true for untapped, attacking, blocking, enchanted, equipped, and targeted. Any counters on a creature are on the switched creature instead.)