Massacre Girl is a rare Legendary Creature — Human Assassin card from Secret Lair Drop (SLD), collector number 1233. Current market price: $36.72 (foil $37.10), TCGplayer market prices via Scryfall.
Menace When Massacre Girl enters, each other creature gets -1/-1 until end of turn. Whenever a creature dies this turn, each creature other than Massacre Girl gets -1/-1 until end of turn.