Serpent of Yawning Depths is a rare Enchantment Creature — Serpent card from Secret Lair Drop (SLD), collector number 1489. Current market price: $24.21, TCGplayer market prices via Scryfall.
Krakens, Leviathans, Octopuses, and Serpents you control can't be blocked except by Krakens, Leviathans, Octopuses, and Serpents.