Astral Siren

Nebulous Form. The Astral Siren adds double its Dexterity modifier to its AC.

Asteroid Dweller. The Astral Siren can merge with a medium size asteroid or boulder. While in the asteroid, the siren cannot be targeted by a spell or attacks.

Stardust. The Astral Siren can move through a space as narrow as 1 inch wide without squeezing.

Unusual Nature. The Astral Siren doesn’t need air, drink, or sleep.

Multiattack. The Astral Siren makes two attacks with its claws.

Claws. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 8 (2d4 + 3) slashing damage and 7 (2d6) psychic damage. 

Luring Song. The Astral Siren sings a magical melody that can even be heard in the vacuum of space. Every humanoid and giant within 300 feet of the siren that can hear the song must succeed on a DC 14 Wisdom saving throw or be charmed until the song ends. The siren must take a 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 toward 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.