Sea Serpent (5e Creature)
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Gargantuan monstrosity, neutral
Hold Breath. The serpent can hold its breath for 1 hour.
Siege Monster. The serpent deals double damage to objects and structures.
Multiattack. The serpent makes two attacks: one with its bite and one with its Constrict. It can't make both attacks against the same target. Instead of making a bite attack, it can use its Swallow.
Bite. Melee Weapon Attack: +14 to hit, reach 15 ft., one target. Hit: 34 (4d12 + 8) piercing damage.
Constrict. Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: 26 (4d8 + 8) bludgeoning damage, and the target is grappled (escape DC 16). Until this grapple ends, the creature is restrained, and the serpent can't constrict another target.
Swallow. The serpent makes one bite attack against a Large or smaller creature it is grappling. If the attack hits, that creature takes the bite's damage and is swallowed, and the grapple ends. While swallowed, the creature is blinded and restrained, it has total cover against attacks and other effects outside the serpent, and it takes 21 (6d6) acid damage at the start of each of the serpent's turns.
Fully grown sea serpents can be longer than ships, and they hunt massive prey. They have been known to attack ships, dragging them beneath the waves with their massive coils, and devouring entire crews in a single gulp, before dragging the husks away to build their nests. They can live for centuries, and a single sea serpent's nest might have ships from eras ago, long thought vanished. Their nests also often have the treasures of their victims, but the sea serpents care little for such trinkets. They lay their eggs in such nests, for even the youngest of newly hatched sea serpents can hold their breath far longer than any land-based humanoid as tides ebb and flow around the nests.