Massacre Girl, Known Killer is a mythic Legendary Creature — Human Assassin card from Murders at Karlov Manor Promos (PMKM), collector number 94p. Current market price: $1.24 (foil $2.93), 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.