Massacre Girl, Known Killer is a mythic Legendary Creature — Human Assassin card from Murders at Karlov Manor (MKM), collector number 94. Current market price: $1.04 (foil $3.52), TCGplayer market prices via Scryfall.
Menace Creatures you control have wither. (They deal damage to creatures in the form of -1/-1 counters.) Whenever a creature an opponent controls dies, if its toughness was less than 1, draw a card.