Polukranos, World Eater is a mythic Legendary Creature — Hydra card from Theros (THS), collector number 172. Current market price: $0.60 (foil $1.54), TCGplayer market prices via Scryfall.
{X}{X}{G}: Monstrosity X. (If this creature isn't monstrous, put X +1/+1 counters on it and it becomes monstrous.) When Polukranos becomes monstrous, it deals X damage divided as you choose among any number of target creatures your opponents control. Each of those creatures deals damage equal to its power to Polukranos.