Coastal Siren

Slippery. The Siren has advantage on ability checks and saving throws made to prevent and escape a grapple.

Can't Charm the Charmer. The Siren has advantage on saving throws against being Charmed.

Universally Beautiful. The Siren appears different and uniquely beautiful to match the tastes of each humanoid the perceives it. Truesight reveals the Siren's true Fey nature.

Tied to the Sea. The Siren cannot willingly leave the water. If forcibly removed, the Siren takes 10 (2d10) necrotic damage every minute until it returns. 

Amphibious. The Siren can breath air and water. 

Luring Song. The Siren sings a magical melody. Every humanoid within 300ft of the siren that can hear the song must succeed on a DC14 Wisdom Saving Throw or be charmed until the song ends. The siren must take bonus action on its subsequent turns to continue singing. It can stop singing at any time. The song ends if the siren is incapacitated. While charmed by the siren, a target is incapacitated and ignores the songs of other sirens. If the charmed target is more than 5 feet away from the siren, the target must move on its turn towards the siren by the most direct route, trying to get within 5 feet. 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 siren, the target can repeat the saving throw. A charmed target can also repeat the saving throw at the end of each of its turns. If the saving throw is successful, the effect ends on it. A target that successfully saves is immune to this siren’s song for the next 24 hours.

Tresses. Melee Weapon Attack. +5 to hit, reach 10ft, one target. Hit: 14 (3d6+4) bludgeoning damage and the target is grappled (escape DC 16 Strength Save) and pulled 5ft towards the Siren. Until this grapple ends, the target is restrained and the Siren cannot use Tresses on another target. If the grapple is successful, the Siren can use Drowning Kiss as a bonus action. 

Drowning Kiss. The Siren presses her lips to the grappled target, sucking the air from their lungs in a moment of passion. The target must succeed on a DC18 Constitution Save. On a failed save, the target will no longer be able to hold their breath underwater until they reemerge on the surface and take a gulp of air.