Large fey (merfolk, shapechanger), neutral

Armor Class 14 (natural armor)
Hit Points 76 (8d10 + 32)
Speed 0 ft. (30 ft. in humanoid form), swim 40 ft.

16 (+3) 14 (+2) 18 (+4) 14 (+2) 16 (+3) 20 (+5)

Skills Deception +8, Perception +5, Performance +8, Persuasion +8, Stealth +5, Survival +6
Damage Immunities cold
Senses darkvision 60 ft., passive Perception 12
Languages Common, Sylvan, Aquan
Proficiency Bonus +3
Challenge 6 (2,300 XP)


  • Amphibious. The ceasg can breathe air and water.
  • Cochull. The ceasg wears a salmon skin, but brighter and more beautiful, which holds the creature’s spirit. The skin has an AC and hit points equal to that of the ceasg, but the garment can’t be directly harmed while the ceasg wears it. If the skin is destroyed, the ceasg becomes poisoned and dies within 1 hour. A ceasg is willing to do anything in its power to recover the skin if it is stolen, including serving the thief.
  • Rejuvenation. If it has a soul egg, a destroyed ceasg gains a new body in 1d10 days, regaining all its hit points and becoming active again. The new body appears within 5 feet of the soul egg.


  • Multiattack. The ceasg makes two attacks, only one of which can be a Bite attack.
  • Bite (Merfolk Form Only). Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 8 (1d10 + 3) piercing damage.
  • Unarmed Strike. Melee Weapon Attack: +6 to hit, reach 10 ft., one creature. Hit: 7 (1d8 + 3) bludgeoning damage. If the target is Medium or smaller, the ceasg can grapple the target (escape DC 14) instead of dealing damage. The target is pulled 5 feet toward the ceasg. Until this grapple ends, the target is restrained, the ceasg tries to drown it, and the ceasg can’t grapple another target. Swallow (Merfolk Form Only). The ceasg makes one bite attack against a Medium or smaller target it is grappling. If the attack hits, the target is swallowed, and the grapple ends. The swallowed target is blinded and restrained, it has total cover against attacks and other effects outside the ceasg, and it takes 10 (3d6) acid damage at the start of each of the ceasg’s turns. The ceasg can have only one target swallowed at a time. If the ceasg dies, a swallowed creature is no longer restrained by it and can escape from the corpse using 5 feet of movement, exiting prone.
  • Change Shape. The ceasg can use its action to polymorph into a Medium humanoid or back into its merfolk form. Its statistics, other than its size, are the same in each form. Any equipment it is wearing or carrying isn’t transformed. It reverts to its merfolk form if it dies.
  • Luring Song. The ceasg sings a magical melody. Every humanoid and giant within 300 feet of the ceasg that can hear the song must succeed on a DC 16 Wisdom saving throw or be charmed until the song ends. The ceasg must take a bonus action on its subsequent turns to continue singing. It can stop singing at any time. The song ends if the ceasg is incapacitated. While charmed by the ceasg, a target is incapacitated and ignores the songs of other ceasgs. If the charmed target is more than 5 feet away from the ceasg, the target must move on its turn toward the ceasg by the most direct route. It doesn’t avoid opportunity attacks, but before moving into damaging terrain, such as lava or a pit, and whenever it takes damage from a source other than the ceasg, a target can repeat the saving throw. A creature can also repeat the saving throw at the end of each of its turns. If a creature’s saving throw is successful, the effect ends on it. A target that successfully saves is immune to this ceasg’s song for the next 24 hours.
  • Wishes. The ceasg’s power to grant wishes is legendary among mortals. Only the most potent ceasgs, such as those among the nobility, can do so. A particular ceasg that has this power can grant one to three wishes to a creature that isn’t a ceasg. Once a ceasg has granted its limit of wishes, it can’t grant wishes again for some amount of time (usually 1 year), and cosmic law dictates that the same ceasg can expend its limit of wishes on a specific creature only once in that creature’s existence. To be granted a wish, a creature within 60 feet of the ceasg states a desired effect to it. The ceasg can then cast the wish spell on the creature’s behalf to bring about the effect.


The ceasg possesses the upper body of a beautiful woman with long hair flowing like seaweed, while her lower body resembles that of a shimmering grilse, the sleek and silvery young salmon. Her eyes gleam like the depths of the sea, and her voice is like a haunting melody.

The ceasg (SEEZG) is a creature of both the sea and freshwater, often found in rivers, streams, and coastal waters. She possesses the ability to shift between her mermaid form and that of a human, allowing her to come ashore. Legends speak of the ceasg granting wishes to those who capture her, though these wishes are more often attempts to secure her freedom. She forms unions with humans and protects her descendants, especially those who venture onto the waters.

The ceasg is not a predator but rather a mystical being with ties to the waters. She doesn’t engage in hunting in the traditional sense, but her enchanting song can draw in and captivate humanoids and giants, luring them to her. This song can have both charming and disorienting effects on those who hear it, making them more susceptible to her influence.

Section 15: Copyright Notice

5E RPG: Celtic Bestiary. Copyright 2023, Mal and Tal Enterprises, LLC; Author Michael Tresca.

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