Aravae "Queen of the Succubi"

Magic Resistance. Aravae has advantage on saving throws against spells and other magical effects.

Shapeshifting. Aravae can alter her physical form at will to that any other medium sized creature. She fully retains her mental capacity no matter her form, and retains the ability to cast spells, even if the form would not normally allow her to do so.

Command over Undeath. Aravae's bloodline relation to Orcus has imbued her with the ability to naturally command all undead around her. Any undead that starts it's turn within 1 mile of her location must make a DC 23 Wisdom saving throw or become charmed by her. Aravae, as a free action, can telepathically communicate with the undead and it must obey her commands. If summoned or conjured by another creature, the undead will still obey the commands of it's original master, but cannot be ordered to damage or hinder Aravae directly. This effect ignores an undead's condition immunities, and lasts until the undead in question moves out of the effects range, is specifically designated by Aravae to be immune to it, or is destroyed.

Attend the Queen. At the start of initiative, Aravae has a 50% chance to summon 1d4 Succubae to assist her in battle. Aravae herself is frozen in initiative order until all of these succubi are removed from the battlefield; she cannot be targeted while this is the case.

Spellcasting. Aravae's spellcasting ability is Charisma (spell save DC 23, +17 to hit with spell attacks). Aravae has access to the following spells:
Cantrips (at will): Chill Touch, Control Flames, Friends, Mage Hand, Mind Sliver, Prestidigitation, Message
1st level (at will): Absorb Elements, Charm Person, Disguise Self, Shield, Faerie Fire, Dissonant Whispers, Sleep
2nd level (at will): Crown of Madness, Phantasmal Force, Scorching Ray, Suggestion, Zone of Truth, Tasha's Mind Whip
3rd level (at will): Counterspell, Fireball, Dispel Magic
4th level (at will): Dimension Door, Greater Invisibility
5th level (3 slots): Dominate Person, Cloudkill
6th level (2 slots): Disintegrate, Globe of Invulnerability, Mental Prison
7th level (2 slots): Power Word Pain 
8th level (1 slot): Power Word Stun
9th level (1 slot): Power Word Kill

Legendary Resistances 3/day. When Aravae fails a saving throw, she may expend 1 Legendary resistance to succeed instead.

Cast a Spell. Aravae can use her action to cast a spell of her choice.

Multiattack. Aravae makes two Soul Drain attacks against separate targets.

Soul Drain. Melee Spell Attack: +15 to hit, reach 5 ft., #1 target. Hit: 38 (5d10 + 8) necrotic damage. Aravae reaches out to grab a creature within range; on a hit, their maximum hit points are reduced by an amount equal to the damage. If this effect causes a creature's maximum hit points to reach 0, they instantly die and Aravae is healed for the damage dealt.

Shattered Psyche (Recharge 6). Aravae attempts to reach into a creature's mind and forcibly break their will. The target must make a Wisdom saving throw against her spell save DC. On a failed save, the target takes 60 (10d10) psychic damage and is stunned for 1 minute; on a successful save, they take half as much damage and are not stunned. A creature stunned by this ability may repeat the save at the end of each of its turns. Sprinkling a vial of Holy Water on a creature affected by this ability will end the effect early. Alternatively, a Greater Restoration or Remove Curse spell will suffice in ending this effect. Once a target saves from this effect, or the effect ends, they are considered immune to this ability for next 24 hours.

Shadow Walk. When Aravae in dim light or darkness, as a bonus action, she can magically teleport up to 120 ft. to an unoccupied space that she can see that is also in dim light or darkness.

Reactionary Spells. Aravae may use her reaction to cast one of the following spells: Shield, Absorb Elements, Counterspell.

Hellish Rebuke (Recharge 5-6). Aravae may use her reaction to cast Hellish Rebuke at 4th level.

Aravae has a total of 5 legendary actions per round.

Cast a Low-Level Spell (Costs 1 Action). Aravae casts a spell of her choice that is 4th level or lower.

Cast a High-Level Spell (Costs 3 Actions). Aravae casts a spell of her choice that is 5th level or higher.

Soul Drain (Costs 2 Actions). Aravae attempts to use Soul Drain on a hostile creature within range.

Recharge Shattered Psyche (Costs 5 Actions). Aravae sacrifices all of her legendary actions for that round to instantly recharge Shattered Psyche.