Balthizar

Legendary Resistance (3/Day). If the dragon fails a saving throw, it can choose to succeed instead.

Damage Resistances. The Dragon has Resistance to necrotic damage.

Skill Proficiency: Stealth. The dragon’s Proficiency Bonus is doubled for its Dexterity (Stealth) checks.

Living Shadow. While in dim light or Darkness, the Dragon has Resistance to damage that isn’t force, psychic, or radiant.

Shadow Stealth. While in dim light or Darkness, the Dragon can take the Hide action as a Bonus Action.

Sunlight Sensitivity. While in sunlight, the Dragon has disadvantage on Attack rolls, as well as on Wisdom (Perception) checks that rely on sight.

Shattered Soul. PC's killed by the dragon can continue to help their allies.  Dead PCs can force a contested charisma roll, if the dragon fails it is stunned until the end of its turn.

Multiattack. The dragon can use its Frightful Presence. It then makes three attacks: one with its bite and two with its claws.

Bite. Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 8 (2d6 + 4) piercing damage plus 10 (5d4) necrotic damage.

Claw. Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 8 (2d6 + 4) slashing damage.

Pneumatic Blast. Ranged Weapon Attack: +12 to hit, reach 20 ft., one target. Hit: 6 (2d4 + 4) bludgeoning damage. DC 16 Athletics or Acrobatics or be knocked back 15 ft and prone.

Frightful Presence. Each creature of the dragon's choice that is within 120 feet of the dragon and aware of it must succeed on a DC 20 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to the dragon's Frightful Presence for the next 24 hours.

Soul Flair (Recharge 5–6). The dragon manifests a 3rd eye dealing radiant damage in a cylinder 15 feet in diameter and 60 feet long. Each creature in that cylinder must make a DC 18 Dexterity saving throw, taking 36 (12d6) radiant damage on a failed save and be blinded until the end of their next turn, or half as much damage on a successful one. Regardless of the save, one Shadow is created adjacent to the affected creature. 

Ego Sheild.  An attack that would hit the dragon is absorbed by an Ego Bearer instead.

The dragon 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. The dragon regains spent legendary actions at the start of its turn.

Detect. The dragon makes a Wisdom (Perception) check.

Pneumatic Blast. The dragon makes a pneumatic blast attack.

Dream Dust (Costs 2 Actions). The dragon beats its wings. Each creature within 10 feet of the dragon must succeed on a DC 18 Charisma saving throw or fall into a magical sleep for one minute. 

Penumbral Dive (Costs 3 Actions). The dragon teleports from one grey ooze pool to another if the pool is within 60 feet.