Annwyn, The Night King. (Bound)

Turning Immunity. Annwyn, even bound, is immune to features that turn undead, unless the spell is cast by the one she is bound to. 

Innate Spellcasting (Psionics). Annwyn's innate spellcasting ability is Wisdom` (spell save DC 17). Annwyn can innately cast the following spells, requiring no components.
(at will): Flame of the Void, Chill Touch, Ray of Frost 
(2/day): Spectral Sentinel, Call to The Grave                                                                                (1/day): Ice Storm

Dispelling Cry. When Annwyn reaches 150 hit points or less she unleashes a dispelling cry. This cry dispels all binding magics that have been placed upon her.

Multiattack Annwyn can attack twice, once with the Void Drinker (if active) and once with shadow strike

Void Drinker Melee Weapon Attack: +7 to hit, reach 5 ft., 1 target. Hit: 13/14 (2d8 + 4 / 2d10 + 4) slashing damage + 3 (1d6) necrotic damage. The necrotic damage is recovered as HP or temporary HP if Annwyn is at full HP. 

Shadow Strike Melee Weapon Attack: +7 to hit, reach 5 ft., 1 target. Hit: 11/13 (2d6 + 4 / 2d8 + 4) slashing damage + 3 (1d6) psychic damage.

Glas Blade Melee Weapon Attack: +7 to hit, reach 5 ft., 1 target. Hit: 13 (2d8 + 4 / 2d10 + 4) slashing damage.

Death Wail. (Recharge 6) Annwyn lets out an ear splitting screech. All creatures within 15ft of her that can hear must make a DC 15 Constitution saving throw. On a fail a creature takes 11 (2d10) psychic damage.  

Change Shape. Annwyn magically polymorphs into a humanoid that has a challenge rating no higher than its own, or back into her true form. She reverts to her true form if she dies. Any equipment she is wearing or carrying is absorbed or borne by the new form (Annwyn's choice).

In a new form, Annwyn retains her alignment, hit points, Hit Dice, ability to speak, proficiencies, Legendary Resistance, and Intelligence, Wisdom, and Charisma scores, as well as this action. Its statistics and capabilities are otherwise replaced by those of the new form, except any class features or legendary actions of that form. However in the new form Annwyn's shadow remains that of her gargantuan form.

Soul Shield (2/Day). If Annwyn is attacked she can choose instead to negate the attack by summoning a 'Wretched Soul' from the either, this then switches the attack target to the soul. When a soul summoned this way is destroyed, the attacker must make a DC 15 Wisdom saving throw or take (4D6+3) from the soul. 

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

Dark Bonds (Costs 3 Actions).  Black spectral chains erupt from the ground in a 100ft sphere with Annwyn at its centre, all creatures within range are instantly restrained unless immune. At the end of their turn a creature can attempt to pass a DC 15 Strength check to break free from the bonds.

Summon Souls (Costs 2 Actions). Annwyn summons 1d4 'Wretched Souls' to a random location that she can see within a 30ft