Serpent of Yawning Depths is a rare Enchantment Creature — Serpent card from Theros Beyond Death (THB), collector number 291. Current market price: $9.76, TCGplayer market prices via Scryfall.
Krakens, Leviathans, Octopuses, and Serpents you control can't be blocked except by Krakens, Leviathans, Octopuses, and Serpents.