Actions

Multiattack. The gloomwater mermaid makes three Gloomwater Harpoon attacks.   Gloomwater Harpoon. Melee or Ranged Weapon Attack: 1d20+7 to hit, reach 5 ft. or range 20/60 ft., one target. Hit: 7 (1d6 + 4) 1d6+4 piercing damage, or 8 (1d8 + 4) 1d8+4 piercing damage if used with two hands to make a melee attack. The harpoon returns to the gloomwater mermaid's hand if used as a ranged weapon.   Tail Slap. Melee Weapon Attack: 1d20+7 to hit, reach 5 ft., one target. Hit: 7 (2d8 + 4) 2d8+4 bludgeoning damage and the target must make a CON save or be stunned until the end of its next turn. A stunned creature holding it breath begins to drown.   Freezing Strikes (Recharge 6). The gloomwater mermaid uses Multiattack. Each attack that hits deals an extra 5 (1d10) 1d10 cold damage. A target that is hit by one or more of these attacks has its speed reduced by 10 feet until the end of the myrmidon's next turn. This effect is cumulative.    

Bonus Action

Siren Song (psionic). The gloomwater mermaid can start a song that persists until she is killed, ends it voluntarily or fails a Constitution saving throw when taking damage as if she was concentrating on a spell. This effect is psionic and is not affected by silence or other sound-based defences. However, spells such as mind blank provide protection.  

• Charm. The gloomwater mermaid targets one humanoid or beast that she can see within 30 feet of her. If the target can see the gloomwater mermaid, it must succeed on a WIS saving throw or be magically charmed. The charmed creature regards the gloomwater mermaid as a trusted friend to be heeded and protected. Although the target isn't under the gloomwater mermaid's control, it takes the gloomwater mermaid's requests or actions in the most favorable way it can. Each time the gloomwater mermaid or its allies do anything harmful to the target, it can repeat the saving throw, ending the effect on itself on a success. Otherwise, the effect lasts 24 hours or until the gloomwater mermaid dies, is on a different plane of existence from the target, or ends the effect as a bonus action. If a target's saving throw is successful, the target is immune to the gloomwater mermaid's Siren Song for the next 24 hours. The gloomwater mermaid can have no more than one humanoid and up to three beasts charmed at a time.
• Song of Lost Glory. The gloomwater mermaid sings a song that fortifies her allies, healing them for 10 (1d10 + 5) points of damage and granting other aquatic allies advantage on their next saving throw or, if under the effect that can be ended by a saving throw, can repeat the saving throw immdieatly and/or at the start of their turn.
• Battle Chant of Atlantis. All allies within 30 feet can use their reaction to move their speed and make a melee attack. If an attack hits, the target is marked and has disadvantage on any attacks (including spells) that do not target the attacker.
• Mournful Keening (1/Day). All hostile creatures within 30 feet must make a CON saving throw or take 6 ( 2d6 ) psychic damage, and the gloomwater mermaid pushes the target 10 feet while each ally may move five feet in response as a free action.

  Innate Spellcasting. The gloomwater mermaid's innate spellcasting ability is Charisma (spell save DC 14). The gloomwater mermaid can innately cast the following spells, requiring no material components:

• At will: druidcraft
• 3/day each: entangle, goodberry
• 1/day each: barkskin, dispel magic, pass without trace, shillelagh, unbearable weight of melancholy (the target must make a WIS saving throw or be burdened by such a weight on their shoulders they cannot move gaining the stunned condition until they successfully save. This effect lasts for 1 minute)

Reactions

Tail Slap. When an attack against a gloomwater mermaid misses she may use tail slap against the triggering target.

Suggested Environments

Aquatic