Shambling Swarm is a rare Creature — Horror card from Torment (TOR), collector number 82. Current market price: $0.47 (foil $5.16), TCGplayer market prices via Scryfall.
When this creature dies, distribute three -1/-1 counters among one, two, or three target creatures. For each -1/-1 counter you put on a creature this way, remove a -1/-1 counter from that creature at the beginning of the next end step.