Massacre Girl is a rare Legendary Creature — Human Assassin card from Duskmourn: House of Horror Commander (DSC), collector number 146. Current market price: $0.47, 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.