Vitreous Choirmaster

medium aberration (crystalline, psionic), lawful-evil · CR fifteen

by Glasswright Voss

Armor Class: 18

Hit Points: 256

Speed: 30 ft., fly 30 ft.

Saving Throws: constitution, intelligence, wisdom, charisma

Damage Immunities: Psychic

Damage Vulnerabilities: Thunder

Condition Immunities: Charmed, Frightened

Senses: blindsight 60 ft., darkvision 120 ft., passive Perception 19

Languages: Common, Deep Speech

Challenge: fifteen

STR 8 (-1)

DEX 16 (+3)

CON 20 (+5)

INT 20 (+5)

WIS 18 (+4)

CHA 22 (+6)

Traits

Magic Resistance. The choirmaster has advantage on saving throws against spells and other magical effects.
Fractured Mind. The choirmaster's awareness is spread across every shard of its crystalline body. It cannot be surprised, is immune to effects that would read its thoughts or sense its emotions, and has advantage on saving throws against being blinded, deafened, or stunned.
Resonant Feedback. Whenever the choirmaster takes thunder damage, its fractures ring in sympathy. Until the end of its next turn, its Shardsong Lash and Keening Bolt each deal an extra 4 (1d8) psychic damage, and the first creature to end its turn within 10 feet of the choirmaster takes 4 (1d8) psychic damage.

Shardsong Lash.
Keening Bolt. On a hit, the target must succeed on a DC 19 Constitution saving throw or be deafened and unable to cast spells with verbal components until the end of its next turn, as its own voice is turned to ringing glass.

Glassward Step. The choirmaster shatters into a swarm of chiming shards and reforms in an unoccupied space it can see within 30 feet. Each creature within 5 feet of the space it leaves must succeed on a DC 19 Dexterity saving throw or take 7 (2d6) slashing damage from flying glass.

Mirror the Voice. The choirmaster attempts to echo the spell back. It makes a Charisma check (DC 10 + the spell's level). On a success, the spell also targets a creature of the choirmaster's choice within range, using the choirmaster's spell save DC. On a failure, nothing happens and this reaction is wasted.

Glass Step. The choirmaster moves up to half its speed without provoking opportunity attacks, its form briefly dissolving into a cloud of drifting shards.
Discordant Verse. The choirmaster sings a chord of shattering glass. Each creature of its choice within 20 feet must succeed on a DC 19 Constitution saving throw or take 16 (3d10) thunder damage and be pushed 10 feet away from the choirmaster. On a successful save, a creature takes half as much damage and isn't pushed.