Turn Immunity. Vlaakith is immune to any effect that turns undead.

Rejuvenation. If Vlaakith is destroyed, she gains a new body in 1d10 days, regaining all her hit points and becoming active again. Her new body appears within 5 feet of her soul vessel.

Undying Will. Whenever Vlaakith fails a saving throw, she can choose to succeed instead. Whenever Vlaakith succeeds on a saving throw in this manner, she regains two fewer legendary actions at the start of her next turn.

Enhance Arcana (1/Turn). Whenever Vlaakith casts uses Spellcasting to cast a spell of 1st level or higher, she can choose to apply one of the following Meta Magic options: Empowered Spell, Heightened Spell, Transmuted Spell, or Twinned Spell.

Master of Magic. Vlaakith's mastery of arcane theorem exceeds all but but the most accomplished arcanists. Vlaakith has advantage on Constitution saving throws made to maintain concentration on spells, and she can maintain concentration on up to two spells at once.

Multiattack. Vlaakith uses Spellcasting, Grasp of the Lich Queen, or Necromantic Eruption (if available). She then makes two Crippling Blast attacks.

Crippling Blast. Melee or Ranged Spell Attack: +18 to hit, reach 5 ft. or range 90 ft., one target. Hit: 23 (3d8 + 10) necrotic damage. If the target is a creature, its speed is halved and it has disadvantage on all ability checks and attack rolls until the end of Vlaakith's next turn.

Dancing Silver Greatsword. Melee Weapon Attack: +18 to hit, reach 5 ft., one target. Hit: 17 (2d6 + 10) slashing damage plus 10 (3d6) psychic damage. This is a magic weapon attack. On a critical hit against a target in an astral body (as with the [spell]astral projection[spell] spell), Vlaakith can cut the silvery cord that tethers the target to its material body, instead of dealing damage.

Grasp of the Lich Queen. Vlaakith combines the might of her arcane, and psionic prowess and lashes out at her assailants. Each creature of Vlaakith's choice that she is aware of within 60 feet of her must make a DC 26 Wisdom saving throw taking 32 (4d10 + 10) psychic damage and is affected by the dominate monster spell for 1 minute on a failed saving throw, or taking half as much damage and not being dominated on a successful save. An affected creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. Whenever a non-affected hostile creature starts its turn within 10 feet of an affected creature, it takes 10 psychic damage.

Spellcasting (Psionics). Vlaakithcasts one of the following spells, requiring no spell components and using Intelligence as the spellcasting ability (save DC 26):

At will: blindness/deafness, blur, detect magic, detect thoughts, dispel magic, magic missile, mirror image
3/day each: dimension door, dominate monster, greater invisibility, hold monster, fireball, nondetection
1/day each: foresight, power word kill, time stop, wish

Necromantic Eruption (Recharge 5-6). Vlaakith unleashes a torrent of negative energy in a 60-foot radius around her. Each creature within the affected area must make a DC 26 Constitution saving throw taking 45 (10d8) necrotic damage on a failed saving throw, or half as much damage on a successful saving throw. If Vlaakith deals damage to at least one creature, she gains advantage on the next ability check, attack roll, or saving throw she makes.

Astral Step. Vlaakith teleports, along with any equipment she is wearing or carrying, up to 60 feet to an unoccupied space she is aware of.

Dancing Silver Greatsword. Vlaakith tosses her silver greatsword into the air, where it makes two attacks against a creature of her choice that she can see within 30 feet of her. Each round on her turn, she can take this bonus action again to have the sword make two attacks on a creature she can see within 30 feet of her, or to call the sword back to her hand. Attacks made with her Silver Greatsword are determined using her Intelligence score.

Banish. As a reaction to being hit by an attack, Vlaakith can magically lash out at the attacker and force it to make a DC 26 Charisma saving throw. On a failed saving throw, an affected creature takes 21 (2d10 + 10) necrotic damage and is banished to harmless demiplane until the start of its next turn. On a successful saving throw, an affected creature takes half as much damage and isn't banished.

Negate Magic. When Vlaakith sees a creature within 60 feet of her casting a spell, she tries to interrupt it. If the creature is casting a spell using a spell slot of 6th level or lower, its spell fails and has no effect. If it is casting a spell of 7th level or higher, it must succeed on a DC 26 Intelligence saving throw, or the spells fails and has no effect.

Vlaakith 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. Vlaakith regains spent legendary actions at the start of her turn.

Strike. Vlaakith makes a Crippling Blast attack.

Psionic Might (Costs 2 Actions). Vlaakith uses Spellcasting, or uses Grasp of the Lich Queen.

Vile Surge (Costs 3 Actions). Vlaakith recharges, or uses her Necromantic Eruption action.