Carried on monochrome wings as black as the void and as bright as a star, the cosmic siren haunts a sphere’s spaceways luring spaceships to their doom or singing a moon’s populace to their final rest, and then feasting on their ruined corpses. Her body is that of a lovely maid save as large as an ogre and with feet that end in sickle-like talons. A flowing, charcoal mane serves as the only clothing she ever wears, her lips stained ruby red by diet, and her eyes smoldering like red dwarves. Unlike a normal siren, she also sports a thick, plummed tail as powerful as any dragons. As the cosmic siren often leads a flock of lesser kin from planet to planet, one might wonder how such a feat as managed as normal sirens are not immune to the rigors of open space. Simply, they charm a ship's crew to carry the flock from place to place until it is time to explode like a flock of bats from their cave to claim new victims.

Cosmic Siren

Large fey, chaotic evil

Armor Class 25 (natural armor)

Hit Points 91 (14d8 + 28)

Speed 30ft

Speed 60ft

Str 15 Dex 26 Con 22 Int 18 Wis 20 Cha 24

Saving Throws Dex +14, Con +12, Cha +13

Skills Deception +13, Persuasion +13

Damage Resistances bludgeoning, piercing, and slashing from nonmagical attacks not made with silvered weapons

Damage Immunities cold, fire

Condition Immunities charmed, poisoned

Senses truesight 120 ft., passive Perception 15

Languages All, telepathy 120 ft.

Challenge 20 (25,000 XP)

Magic Resistance.

The cosmic siren has advantage on saving throws against spells and other magical effects.

Magic Weapons.

The cosmic siren's weapon attacks are magical.

Sensual Aura.

Any creature hostile to the cosmic siren that starts its turn within 20 feet of the pit fiend must make a DC 21 Wisdom saving throw, unless the fey is incapacitated. On a failed save, the creature is Charmed by the siren until the start of its next turn. If a creature's saving throw is successful, the creature is immune to the cosmic siren's Sensual Aura for the next 24 hours.

Siege Monster.

The cosmic siren deals double damage to objects and structures.

Actions

Multiattack.

The cosmic siren makes four attacks, two with its claws and two with its tail. Alternatively, the cosmic siren can shriek twice.

Claw.

Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: 17 (2d8 + 8) slashing damage.

Tail.

Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: 24 (3d10 + 8) bludgeoning damage.

Shriek.

Ranged Spell Attack: +13 to hit, range 300/900 ft., one target. Hit: 22 (4d10) thunder damage.

Luring Song.

The cosmic siren sings a magical melody. Every humanoid and giant within 300 feet of the siren that can hear the song must succeed on a DC 21 Wisdom saving throw or be charmed until the song ends. The cosmic 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 cosmic siren, the target must move on its turn towards the cosmic 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 cosmic 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 cosmic siren’s Luring Song for the next 24 hours.

Ennui Song.

The cosmic siren sings a magical melody. Every humanoid and giant within 300 feet of the siren that can hear the song must succeed on a DC 21 Charisma saving throw or take 22 (4d10) psychic damage at the end of each its turn until the song ends. The cosmic 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. for the duration, a target is incapacitated and ignores the songs of other sirens. An affected creature repeats 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 cosmic siren’s Ennui Song for the next 24 hours.