Sea Serpent

Family: Aquatic & Fish

Gargantuan beast, unaligned

Armor Class 16 (natural armor)
Hit Points 217 (15d20 + 60)
Speed 20 ft., swim 60 ft.

24 (+7) 14 (+2) 19 (+4) 3 (-4) 11 (+0) 11 (+0)

Saving Throws Str +11, Con +8
Skills Perception +4, Stealth +6
Damage Resistances fire
Damage Immunities cold
Senses darkvision 120 ft., passive Perception 14
Challenge 12 (8,400 XP)

Special Traits

  • Elusive. When not in combat, a sea serpent cannot be detected by divination magic or seen through scrying.
  • Legendary Resistance (1/Day). If the sea serpent fails a saving throw, it can choose to succeed instead.
  • Siege Monster. The sea serpent deals double damage to objects and structures.
  • Water Breathing. The sea serpent can breathe only underwater.


  • Multiattack. The sea serpent makes two attacks: once with its bite and once with its constrict.
  • Bite. Melee Weapon Attack: +11 to hit, reach 20 ft., one target. Hit: 25 (4d8 + 7) piercing damage.
  • Constrict. Melee Weapon Attack: +11 to hit, reach 20 ft., one target. Hit: 21 (4d6 + 7) bludgeoning damage, and the target is grappled (escape DC 21). Until this grapple ends, the creature is restrained, and the sea serpent can’t constrict another target.
  • Elusive Dive. The sea serpent takes the Dash action, and until the beginning of its next turn, it gains a +10 bonus on Dexterity (Stealth) checks and cannot be tracked by nonmagical means.

Legendary Actions

A sea serpent can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. A sea serpent regains spent legendary actions at the start of its turn.

  • Detect (Costs 1 Action). The sea serpent makes a Wisdom (Perception) check.
  • Surge (Costs 1 Action). The sea serpent swims its base movement rate, without provoking opportunity attacks.
  • Tail Slap (Costs 2 Actions). The sea serpent makes a melee attack: +11 to hit, reach 20 ft., one target. Hit: 21 (4d6 + 7) bludgeoning damage, and the target must make a DC 19 Strength saving throw. On a failed save, the target is knocked prone.


Tales of immense sea serpents have colored the accounts of seagoing folk since the first ship sailed beyond sight of land. Yet proof of these immense and elusive creatures is remarkably difficult to come by, for not only is the ocean vast and the true sea serpent rare, but these creatures are quite adept at both avoiding capture and destroying ships bent on such a daunting task. Due to the sea serpent’s hermitic nature, many sailors take to ascribing the sighting of such a beast to an omen, although whether the sighting portends peril or providence depends as much upon the ship’s morale as it does anything else-the sea serpent itself has little interest in prophecy, and only its hunger determines how dangerous its proximity to a curious ship can be. Deadly danger surely awaits, however, when its spine-frilled neck arches up from the water like a snake ready to strike.

Section 15: Copyright Notice

Sea Monsters (5E) © 2021, Legendary Games; Authors Michael Ritter, Michael “solomani” Mifsud, Robert J. Grady, Mark Hart, Jeff Ibach, Alex Riggs, Scott D. Young, Jeff Lee, Matt Kimmel, and Jason Nelson.

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