Amphibious. The melusine can breathe air and water

Innate Spellcasting. The melusine's innate spellcasting ability is Wisdom (spell save DC 14). The melusine can innately cast the following spells, requiring no components.

• 2/day: detect thoughts, dominate person, sleep

Shapechanger. As an action, the melusine can shapechange into a medium female humanoid, or back into its true form. If the melusine dies, it reverts to its true form.

Multiattack. The melusine uses Acid Stream and makes two attacks: one with its claws and one with its tail.

Claws. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 18 (4d6 + 4) slashing damage.

Tail. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 15 (2d10 + 4) bludgeoning damage.

Acid Stream. The melusine shoots out a 5-foot wide stream of acid in a 30-feet long line. Each creature in the line must succeed on a DC 17 Dexterity saving throw or be covered in acid for the spell’s duration or until a creature uses its action to scrape or wash the acid off itself or another creature.  A creature covered in the acid takes 22 (4d8 + 4) acid damage at the start of each of its turns.

Luring Song. The melusine sings a magical melody. Every humanoid and giant within 300 feet of the melusine that can hear the song must succeed on a DC 11 Wisdom saving throw or be charmed until the song ends. The melusine must take a bonus action on its subsequent turns to continue singing. It can stop singing at any time. The song ends if the melusine is incapacitated.

While charmed by the melusine, a target is incapacitated and ignores the songs of other creatures. If the charmed target is more than 5 feet away from the melusine, the target must move on its turn toward the melusine 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 melusine, 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 melusine's song for the next 24 hours.