Name: Cirein-cròin
Large monstrosity, neutral
Armor Class: 14 (natural armor)
Hit Points: 136 (16d10 + 48)
Speed: 30 ft., swim 50 ft.

STR: 19 (+4)
DEX: 14 (+2)
CON: 16 (+3)
INT: 6 (-2)
WIS: 10 (+0)
CHA: 7 (-2)

Skills: Perception +4, Stealth +4
Senses: Darkvision 60 ft., passive Perception 14
Languages: understands Common and Gaelic but can't speak

        Amphibious: The Cirein-cròin can breathe air and water.
        Keen Smell: The Cirein-cròin has advantage on Wisdom (Perception) checks that rely on smell.
        Multiattack: The Cirein-cròin can use its Frightful Presence. It then makes two attacks: one with its bite and one with its tail.
        Bite: Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 18 (4d6 + 4) piercing damage.
        Tail: Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 14 (3d6 + 4) bludgeoning damage. If the target is a creature, it must succeed on a DC 16 Strength saving throw or be knocked prone.
        Frightful Presence: Each creature of the Cirein-cròin's choice within 30 feet of it and aware of it must succeed on a DC 14 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to the Cirein-cròin's Frightful Presence for the next 24 hours.

Legendary Actions
The Cirein-cròin can take 3 legendary actions, choosing from the options below. Only one legendary action can be used at a time and only at the end of another creature's turn. The Cirein-cròin regains spent legendary actions at the start of its turn.
        Bite: The Cirein-cròin makes a bite attack.
        Tail: The Cirein-cròin makes a tail attack.
        Swim: The Cirein-cròin moves up to its swim speed without provoking opportunity attacks.

Description: The Cirein-cròin is a fearsome sea creature from Scottish folklore, said to dwell in the depths of the ocean. It is described as a large, serpentine beast with a scaly body that is covered in a thick layer of slime. Its head is somewhat dog-like, with sharp teeth and a pair of small, beady eyes that gleam in the darkness.

The creature's body is long and sinuous, measuring up to 60 feet in length, with a thick, powerful tail that it uses to propel itself through the water. Its skin is a dark, mottled green and brown, which helps it to blend in with the seaweed and rocks on the ocean floor.

The Cirein-cròin's most distinctive feature, however, is the large, fan-shaped fin that runs down the length of its back. This fin is said to be incredibly strong, and it allows the creature to swim at great speeds and change direction quickly, making it a formidable opponent for any who dare to cross its path.

Those who have encountered the Cirein-cròin in the wild report that it emits a loud, eerie screech that echoes through the water, causing even the bravest of sailors to tremble in fear. Some say that the sound is so terrifying that it can shatter glass and damage the eardrums of those who hear it.

Overall, the Cirein-cròin is a mysterious and frightening creature that has captured the imaginations of Scottish storytellers for centuries. Its powerful body and deadly presence make it a creature to be feared, respected, and avoided at all costs.