Arcanya Devil

Durable Magic. While the Arcanya maintains concentration on a spell, it has a +2 bonus to AC and all saving throws.

Tactical Wit. The Arcanya gains a bonus to your initiative rolls equal to her Intelligence modifier (+6).

War Caster. The Arcanya has advantage on CON saving throws that you make to maintain her concentration on a spell when she takes damage. She can perform the somatic components of spells even when she has weapons or a shield in one or both hands.

Twin Mind. The Arcanya has the ability to concentrate on up to two concentration spells at once.

Spellcasting. An Arcanya is a 19th-level spellcaster. Her spellcasting ability is Intelligence (spell save DC 20, +12 to hit with spell attacks). Kaiah has the following wizard spells prepared:
Cantrips (at will): Dancing Lights, Fire Bolt, Mage Hand, Prestidigitation, Shocking Grasp
1st level (4 slots): Chromatic Orb, Detect Magic, Find Familiar (R), Identify (R), Shield (At will), Unseen Servant (R), Witch Bolt.
2nd Level (3 slots): Blindness/Deafness, Enlarge/Reduce, Invisibility (At will), Shadow Blade, Suggestion, Tasha's Mind Whip
3rd Level (3 slots): Blink, Counterspell, Dispel Magic, Fireball, Haste, Lightning Bolt, Sending
4th Level (3 slots): Banishment, Dimension Door, Fabricate, Gravity Sinkhole, Greater Invisibility, Polymorph
5th Level (3 slots): Bigby's Hand, Cone of Cold, Des's Shadow Barrage, Passwall, Seeming, Telekinesis
6th Level (2 slots): Chain Lightning, Disintegrate, Flesh to Stone, Sunbeam, Truesight
7th Level (1 slot): Finger of Death, Forcecage, Magnificent Mansion, Teleport
8th Level (1 slot): Dominate Monster, Feeblemind, Illusory Dragon
9th Level (1 slot): Blade of Disaster, Gate,

Hellfire Dagger. Melee Weapon Attack: +10 to hit, reach 5 ft., range 20/60 ft., one target. Hit: 7 (1d4 + 4) piercing damage. In addition, any humanoid killed by an attack made with this weapon has its soul funneled into the River Styx, where it’s reborn instantly as a lemure devil (described in the Monster Manual).

Off-hand attack. If the Arcanya uses their action to cast a spell, she can use her bonus action to attack with their Hellfire Dagger.

Second Wind. Once per short rest, the Arcanya can use a bonus action to regain 1d10 + 1 HP.

War Caster. The Arcanya can use its reaction to make an opportunity attack to cast a spell that has a casting time of 1 action and targets only that creature.