Ancient Aether Dragon

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

Multiattack. The dragon can use it's Frightful Presence. It then makes three attacks.

Bite. Melee Weapon Attack: +16 to hit, reach 10ft., one target. Hit: 17 (2d10+6) piercing damage. 

Claw. Melee Weapon Attack: +16 to hit, reach 10ft., one target. Hit: 12 (2d6+6) slashing damage.

Tail. Melee Weapon Attack: +16 to hit, reach 20ft., one target. Hit: 15 (2d8+6) bludgeoning damage.

Frightful Presence. Each creature of the dragon's choice that is within 120ft of the dragon and is aware of it must succeed 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 on it, the creature is immune to the dragon's Frightful Presence for 24 hours.

Aether Breath (Recharge 5-6). The dragon exhales a 90ft cone of raw blue tinged Aether. Each creature in that area must succeed a DC 22 Dexterity saving throw , taking 8d10 fire damage and 8d10 acid damage on a failed save, or half as much on a success.

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 it's turn.

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

Tail Attack. The dragon makes a Tail attack.

Wing Attack (Costs 2 actions). The dragon beats it's wings. Each creature within 10 feet of it must succeed on a DC 24 Dexterity saving throw or take 12 (2d6+7) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.