Balorus

Mobility. At the end of Balorus's turn, roll a d4. That roll is how many reactions Balorus can take until his next turn.

Whispers of the Ancients. Balorus himself cannot speak, but he has learned to cast spells without the verbal component. He communicates by summoning whispers that speak the languages he understands. They are difficult to understand, and often require an insight or perception check to understand. 

Advanced War Caster. Balorus makes Concentration checks at advantage, can cast 2 leveled spells in one turn, and can maintain two concentration spells at once. Balorus makes Concentration checks for both spells when he takes damage. He also has resistance to spell damage, but this effect does not apply to thunder damage spells.

Spellcasting. Balorus is a 12th-level spellcaster. Its spellcasting ability is CHA (spell save DC 19, +11 to hit with spell attacks). Balorus has following spells prepared:
Cantrips (at will): Fire bolt, Eldritch Blast, Shocking Grasp, Acid Splash, Mind Sliver, prestidigitation
1st level (5 slots): Mage Armor*, Burning Hands, Magic Missile, Shield, Absorb Elements, Guiding Bolt, Inflict Wounds, Disguise Self
2nd level (4 slots): Hold Person, Detect Thoughts, Mirror Image*, Tasha's Mind Whip, Spiritual Weapon, Suggestion
3rd level (4 slots): Fireball, Enemies Abound, Pulse Wave, Slow, Counterspell, Dispel Magic, Vampiric Touch
4th level (3 slots): Blight, Confusion, Dimension Door, Resilient Sphere, Greater Invisibility, Storm Sphere
5th level (3 slots): Contagion, Modify Memory, Wall of Force, Synaptic Static, Eyebite, Immolation, Dominate Person
6th level (3 slots): Programmed Illusion, Guards and Wards, Disintegrate, Forbiddance, Harm
7th level (2 slots): Prismatic Spray, Project Image, Delayed Blast Fireball

*These spells are cast at the beginning of combat

Magic Resistance. Balorus has advantage on saving throws against magical effects. This ability does not apply to banishing magic. Balorus has disadvantage on saving throws against banishing magic. 

Magic Defense. If Balorus takes more than 50 points from one attack, the attacker must make a DC 20 WIS saving throw. On a failed save, the attack does no more than 50 points of damage. 

Mired Movement. Balorus can cast Misty Step without expending any spells slots. He can do this 4 times a day.

Multiattack. Balorus can cast 1 leveled spell and one cantrip in an action. Alternatively, Balorus can make one Prismatic Wrath attack, and cast one cantrip.

Dagger. Melee Weapon Attack: +9 to hit, reach 5 ft., 1 target. Hit: (1d4 + 4) piercing damage.

Prismatic Wrath. Ranged Weapon Attack: +12 to hit, range 100/150 ft., 2 targets. Hit:  (6d6 + 6) radiant damage. On a hit, the targets must make a DC 15 CON save or be blinded until the beginning of Balorus' next turn. 

Reality Tear. When a creature succeeds on a saving throw within 60 feet of Balorus, he can use a reaction to make that creature make a DC 20 WIS save. On a failed save, the creature suffers a -5 to the original save they made.