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Sea Serpent


AC 17 (natural armor)

HP 247 (15d20 + 90; bloodied 123)

Speed 10 ft., swim 50 ft.

Proficiency +5; Maneuver DC 22

Saving Throws Con +11, Dex +5, Int +2, Wis +7, Cha +4

Senses darkvision 60 ft., passive Perception 12


Amphibious. The serpent can breathe air and water.

Reactive. The serpent can take two reactions per round, one with its tail and one with its bite. It can’t take two reactions on the same turn.

Sinuous. The serpent can share the space of other creatures and objects.


Coils. Melee Weapon Attack: +14 to hit, reach 5 ft., one Large or larger target in its space. Hit: 51 (4d20 + 9) bludgeoning damage. If the target is a creature, it is grappled (escape DC 22). If the target is an object, it is held. Until the grapple or hold ends, the target’s speed is reduced to 0, and the sea serpent’s coils attack automatically hits the target. If an attacker subjects the serpent to a critical hit, this grapple or hold ends.

Tail. Melee Weapon Attack: +14 to hit, reach 15 ft., one target. Hit: 27 (4d8 + 9) bludgeoning damage. If the target is a creature, it makes a DC 22 Strength saving throw . On a failure, it is pushed up to 15 feet away from the serpent and knocked prone .

Bite. Melee Weapon Attack: +14 to hit, reach 15 ft., one target. Hit: 31 (4d10 + 9) piercing damage.

Thrash (While Bloodied ). The serpent moves up to its speed and then attacks with its tail and its bite.

Recover (1/Day, While Bloodied ). The serpent ends one condition or effect on itself.


Reactive Bite. If the serpent takes 15 damage or more from a melee attack made by a creature it can see, it bites the attacker.

Reactive Tail. If the serpent takes 15 damage or more from an attack made by a creature or object it can see, it makes a tail attack against the attacker.

Vehicle Combat

The serpent attacks a Huge or larger target, such as a ship. It moves into the target’s space and attacks with its coils. It ignores small targets, such as passengers, unless it takes 15 damage or more from a single hit. It bites melee combatants and tail-swipes ranged attackers, such as archers or ballistas, trying to knock them into the water. The serpent temporarily disengages when it is subjected to a melee critical hit, but it doesn’t flee the battle until it is conditions|bloodied]]. If it takes significant damage while it’s fleeing, it fights to the death with its Thrash action, targeting the Large and smaller creatures that torment it.

Underwater Combat

The serpent ignores Large or smaller creatures unless attacked. If antagonized, it uses its action to bite and its two reactions to further punish attackers. It won’t retreat but allows creatures to flee once it’s bloodied .

Legends and Lore

With a History or Nature check, characters can learn the following:

DC 10 A sea serpent attack is a ship captain’s greatest fear. A sea serpent wraps its coils around a ship, slowly crushing it to pieces. It usually ignores a ship’s passengers unless they deal significant damage.

DC 15 A sea serpent flees when seriously wounded. A ship’s crew may also cause a sea serpent to loose its coils by striking a lucky blow with an axe, sword, or other melee weapon. A fleeing serpent usually dives down to its treasure-strewn lair.


Longer than any sailing vessel, the sea serpent is a scaled snake with a dragon-like head. It is capable of splintering ships in its coils and forcing the wreckage beneath the waves. 

Deep Sea Danger. Nearly every blue-water sailor has a story, true or false, of an encounter with a sea serpent. Some have merely spied one from a distance, while others claim to have had their ship smashed to kindling by a serpent’s embrace. Few have battled a sea serpent and sailed a whole ship back to port.

Once a sea serpent has scuttled a vessel, it disappears beneath the waves. It has no interest in eating the crew. It attacks ships only because they are the size of its usual prey: whales, giant squid, and other deep-sea behemoths.

Undersea Treasure. A sea serpent’s habit of sinking ships means that treasure accumulates on the ocean floor around its hunting grounds. Adventurers who follow a wounded sea serpent to its lair find the sea floor strewn with sunken ships and forgotten gold.


1–2 Attacks Huge and larger creatures or vehicles

3 Swimming in the distance; ignores travelers

4 Rears up nearby and then dives; may follow vehicles underwater, attacking them later


Sea serpents are deep sea hunters. 

CR 5–16 sea serpent

Treasure 2,000 gp, 10 pearls (100 gp each), 5 life-sized bronze statues (250 gp each), potion of supreme healing , staff of thunder and lightning , wind fan

CR 31+ 2 sea serpents

Treasure 1,000 pp, 15,000 gp, 10 pieces of fine jewelry (750 gp each), magical sentient ship’s figurehead that fights as a treant (25,000 gp), 12 3 arrows , 6 3 ballista bolts , ring of water elemental command , 2 scale mail

Monster Type Description

Monstrosities are magical beings usually native to the Material Plane. Some monstrosities combine the features of beasts and humanoids, like centaurs . Others have bizarre or unnatural appearances, like many-tentacled ropers . Monstrosities could only arise in a world suffused with magic.