Gloom Ripper is a rare Creature — Elf Assassin card from Lorwyn Eclipsed Promos (PECL), collector number 102p. Current market price: $0.30 (foil $1.05), TCGplayer market prices via Scryfall.
When this creature enters, target creature you control gets +X/+0 until end of turn and up to one target creature an opponent controls gets -0/-X until end of turn, where X is the number of Elves you control plus the number of Elf cards in your graveyard.