Crystalline Siren

 Crystalline Form: The Crystalline Siren is immune to the Poisoned condition and Poison damage. It has Resistance to Piercing and Slashing damage. It has Vulnerability to Bludgeoning damage.

Keen Senses: The Siren adds her proficiency bonus (+3) to her initiative rolls.

Irresistible Allure (Recharge 5-6): The Crystalline Siren can project an aura of overwhelming desire. As an action, each creature of the Siren's choice within 30 feet that can see or hear the Siren must succeed on a DC 17 Wisdom saving throw or be charmed by it until the end of its next turn. While charmed in this way, a creature is incapacitated and has a speed of 0. If the Siren takes damage, this effect ends on all charmed creatures.

Shifting Facets: The Crystalline Siren has advantage on Dexterity (Stealth) checks while in areas with dim light or shadows, or when surrounded by crystalline formations.

Legendary Resistance (3/Day): If the Crystalline Siren fails a saving throw, it can choose to succeed instead.

 Multiattack: The Siren makes two Crystal Claw attacks. It can replace one attack with Crystal Embrace.

Crystal Claw: Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 9 (1d10 + 4) slashing damage.

Crystal Embrace: Melee Weapon Attack: +8 to hit, reach 5 ft., one creature. Hit: 7 (1d6 + 4) piercing damage, and the target is grappled (escape DC 16) and restrained. The Siren can only grapple one creature at a time in this way.

Soul Siphon: While grappling a creature, the Siren can use this action. The grappled creature must make a DC 16 Constitution saving throw, taking 14 (4d6) necrotic damage on a failed save, or half as much on a successful one. The Siren regains hit points equal to the necrotic damage dealt.
The Crystalline Siren can use this action as part of Crystal Embrace if the target got grappled in the same turn.

Crystal Glide: The Crystalline Siren can use a bonus action to Disengage or move up to half its speed (15 feet) without provoking opportunity attacks. This movement does not need to be in a straight line.

Alluring Glimmer: When a creature within 60 feet of the Crystalline Siren hits it with an attack, the Siren can use its reaction to cause its crystalline form to briefly shimmer with intense, captivating light. Each creature of your choosing within 30 feet must succeed on a DC 15 Wisdom saving throw or be charmed by the Siren until the end of its next turn. While charmed this way, the creature has disadvantage on attack rolls.

The Crystalline Siren can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. The Crystalline Siren regains spent legendary actions at the start of its turn.

Siren's Call (1 action): One creature charmed by the Siren that it can see or hear uses its reaction to move up to its speed toward the Siren. Alternatively, one creature not charmed by the Siren within 30 feet must succeed on a DC 17 Wisdom saving throw or be Charmed by the Siren until the end of its next turn.

Crystal Step (1 action): The Siren magically teleports up to 30 feet to an unoccupied space it can see.

Whispering Drain (2 actions): One creature the Siren can see within 60 feet must make a DC 16 Constitution saving throw, taking 7 (2d6) necrotic damage on a failed save, or half as much on a successful one. The Siren regains hit points equal to the necrotic damage dealt.

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