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Sea Serpent

Sea Serpent
Public Domain,

The sea serpent is a tremendous seafaring monster of great length and power. They vary in appearance, some looking like snakes with minor fins and gill slits, others improbable lengths of scaly body with peculiar fins, humps, ridges, and earless horse-like heads and shaggy manes.

Sea serpents are large beasts of varying temperaments. Some are peaceable creatures that playfully weave their way through the waters, supping on fish and kelp and occasionally taking following passing ships with mild interest.

Others are ferocious and territorial monsters that attack ships, crushing them to pieces and then devouring sailors from the wreckage at their leisure, or simply ripping apart all manner of man or beast that comes their way. Some rare ones appear to be compassionate and friendly critters who enjoy playing with swimmers, saving drowning men, chasing large schools of fish into the nets of fishermen, offering pearls and other treasures of the ocean, and using their magical powers to ensure good sailing for vessels.

They live in rocks along the coast sunning their scales on the ocean surface and will crawl inland to feed on calves, lambs and hogs.

Spine-frilled neck arching up from the water like a snake ready to strike, this ship-sized serpent hisses a challenge.

Sea Serpent

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
Languages –
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.
  • BiteMelee Weapon Attack: +11 to hit, reach 20 ft., one target. Hit: 25 (4d8 + 7) piercing damage.
  • ConstrictMelee 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.

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.

Sea Serpent CR 12
XP 19,200

N Gargantuan magical beast (aquatic)

Init +6; Senses Darkvision 120 ft., Low-Light Vision; Perception +8
AC 25, touch 8, flat-footed 23 (+2 Dexterity, +17 natural, -4 size)

hp 187 (15d10+105)

Fort +16, Ref +13, Will +7

Defensive Abilities

elusive; Immune cold; Resist fire 30
Speed 20 ft., Swim 60 ft.

Melee bite +23 (4d8+22/19-20 plus grab), tail slap +18 (3d6+6 plus grab)

Space 20 ft.; Reach 20 ft.

Special Attacks capsize, constrict (3d6+18), swallow whole (4d8+18 bludgeoning damage, AC 18, hp 18)
Strength 34, Dexterity 14, Constitution 25, Intelligence 2, Wisdom 11, Charisma 11

Base Atk +15; CMB +31 (+35 grapple); CMD 43 (can’t be tripped)

Feats Improved Bull Rush, Improved critical (bite), Improved Initiative, Iron Will, lightning reflexes, Power Attack, Skill Focus (Stealth), Stealthy

Skills Perception +8, Stealth +13, Swim +20
Environment any ocean

Organization solitary

Treasure none
Special Abilities
Capsize (Ex)   A sea serpent can attempt to capsize a boat or ship of its size or smaller by ramming it as a charge attack and making a combat maneuver check. The DC of this check is 25 or the result of the boat captain’s Profession (sailor) check, whichever is higher.  

Elusive (Su) Sea serpents have long been the stuff of maritime legends, but despite countless attempts to hunt them, they are rarely encountered unless they wish it. As a full-round action while in water, a sea serpent can move up to its run speed (300 ft.) without leaving any trace of its passing (identical in effect to a pass without trace).

An elusive sea serpent gains a +40 circumstance bonus to its Stealth check. In addition, except when in combat, a sea serpent is considered to be under the effects of a nondetection spell. Both of these spell effects are at caster level 20th and cannot be dispelled.
Sea Serpent

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 their 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.  

Although the creatures are little more than animals, they possess about them an air of mysticism that even old salts and cynics are forced to admit quickens the heart and buoys (or sinks) the spirit. Reports of sightings are just as likely to encourage travel as they are to cause panic among seafarers, as explorers and adventurers flock to the site in hopes of sighting such a legendary creature.  

Typical specimens are 60 feet in length and weigh 4,500 pounds, but their upward size limit is unknown. Certainly, the sea is a vast and mysterious place more than capable of supporting whales and other such leviathans, and tales of sea serpents that exceed lengths of 300 feet or more are not unheard of. You can generate statistics for a sea serpent of such tremendous size by applying the advanced simple template or the giant simple template to the statistics presented here. Alternatively, you can advance this sea serpent to Colossal size, increasing its Hit Dice to 25 and its CR to 18.

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