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

Magic Resistance. The void dragon has advantage on saving throws against spells and other magical effects.

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

Bite. Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: 19 (2d10 + 8) piercing damage plus 7 (2d6) fire damage.

Claw. Melee Weapon Attack: +14 to hit, reach 5 ft., one target. Hit: 15 (2d6 + 8) slashing damage.

Tail. Melee Weapon Attack: +14 to hit, reach 15 ft., one target. Hit: 17 (2d8 + 8) bludgeoning damage.

Mind-melting Presence. Each creature of the void dragon's choice that is within 120 feet of the void dragon and aware of it must succeed on a DC 19 Sanity saving throw or roll once on the short term madness table. Regardless of the outcome, the creature is immune to this affect for 24 hours. 

Void Breath (Recharge 5–6). The void dragon exhales negative energy in a 100 ft. line. Each creature in that area must make a DC 21 Dexterity saving throw, taking 63 (18d6) necrotic damage on a failed save, or half as much damage on a successful one.

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

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

Tail Attack. The void dragon makes a tail attack.

Wing Attack (Costs 2 Actions). The void dragon beats its starry wings. Each creature within 10 feet of the void dragon must succeed on a DC 22 Dexterity saving throw or take 15 (2d6 + 8) bludgeoning damage and be knocked prone. The void dragon can then fly up to half its flying speed.