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

Silence The Earth. A sphere with a 500 foots radius  is centered on the dragon where Silence is in constant effect.

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: +11 to hit, reach 10 ft., one target. Hit: 17 (2d10 + 6) piercing damage.

Claw. Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 13 (2d6 + 6) slashing damage.

Tail. Melee Weapon Attack: +11 to hit, reach 15 ft., one target. Hit: 15 (2d8 + 6) bludgeoning damage.

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 16 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.

Breath Weapons (Recharge 5–6). The dragon uses a pure magic breath weapons in a 60-foot cone. Each creature in that area must make a DC 18 Constitution saving throw, taking 46 (12d6) force damage on a failed save, or half as much damage on a successful one.

Cast Greater Invisibility. The dragon can cast Greater Invisibility at will, making an attack will end the effect. 

Achromatic Wave. (Recharge 11–12) The dragon in center impacts magic energy wave in a 60-foot sphere. Each creature in that area make a DC 18 Dexterity saving throw, on a failed save they take 50(14d6) force damage 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 its 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 its wings. Each creature within 10 feet of the dragon must succeed on a DC 19 Dexterity saving throw or take 13 (2d6 + 6) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.