Gargos, Vicious Watcher is a rare Legendary Creature — Hydra card from Core Set 2020 Promos (PM20), collector number 172p. Current market price: $1.62 (foil $1.31), TCGplayer market prices via Scryfall.
Vigilance Hydra spells you cast cost {4} less to cast. Whenever a creature you control becomes the target of a spell, Gargos fights up to one target creature you don't control.