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

Magic Desynchronization: The Void Dragon is not of this reality and operates on a different wavelength of power. If affected by an arcane spell the Void Dragon must make a DC 20 Wis save or be unable to use his magic until the end of his next turn.

Humanoid Form: A void dragon may polymorph at will into any humanoid of any description, though often preferring a single form. In this form their AC becomes 15 (natural armor) and size becomes medium. In this form they are treated as both humanoid and dragon. Additionally if a Void dragon is effected by arcane magic in this form they cannot change form again until the end of the next round. 

Multiattack. The dracolich 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: 18 (2d10 + 7) piercing damage plus 5 (1d10) lightning damage.

Claw. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 14 (2d6 + 7) slashing damage.

Tail. Melee Weapon Attack: +8 to hit, reach 15 ft., one target. Hit: 16 (2d8 + 7) bludgeoning damage.

Frightful Presence. Each creature of the dracolich’s choice that is within 120 feet of the dracolich and aware of it must succeed on a DC 18 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 dracolich’s Frightful Presence for the next 24 hours.

Negative Breath (Recharge 5–6). The dracolich exhales negative energy in a 90-foot line that is 5 feet wide. Each creature in that line must make a DC 20 Dexterity saving throw, taking 66 (12d10) necrotic damage on a failed save, or half as much damage on a successful one.

Negative Magic: May cast the following spells at will in place of an attack:

Vampiric Touch(5th): at a range of 60ft, automatically does max damage to Undead under the Void Dragon's control.

Enervation(5th): this spell is not considered concentration and can be applied multiple times, damage does not take a subsequent action to trigger. The save may be made again whenever additional damage is done with this spell. 

Shadow of Moil(5th): this spell does not require concentration.

Undead Dominion: Undead within 120ft are automatically leashed to the Dragon's will. Intelligent undead can make a DC 22 Cha save to become immune to this.

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

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

Tail Attack. The dracolich makes a tail attack.

Wing Attack (Costs 2 Actions). The dracolich beats its tattered wings. Each creature within 10 feet of the dracolich must succeed on a DC 21 Dexterity saving throw or take 14 (2d6 + 7) bludgeoning damage and be knocked prone. After beating its wings this way, the dracolich can fly up to half its flying speed.