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

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

Bite. Melee Weapon Attack: +4 to hit, reach 10 ft., one target. Hit: 15 (2d10 + 4) piercing damage

Tail. Melee Weapon Attack: +10 to hit, reach 20 ft., one target. Hit: 9 (d8 + 4) bludgeoning damage.

 Innate Spellcasting (Psionics). The dragon's innate spellcasting ability is Intelligence (spell save DC 17). It can innately cast the following spells, requiring no components:
At Will: mind thrust
1/day each: scrying, telekinesis, teleportation circle

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 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 dragon's Frightful Presence for the next 24 hours.

Breath Weapons (Recharge 5–6). The dragon uses one of the following breath weapons.

Astral Breath. The dragon exhales an astral beam in a 120-foot beam. Each creature in that area must make a DC 20 Dexterity saving throw, taking 50 (10d8) force damage on a failed save, or half as much damage on a successful one.

Halting Aura. The dragon exudes a debilitating aura in a 30-foot area centered on itself. Each creature in that area must succeed on a DC 16 Wisdom saving throw or be affected for the duration.

An affected target's speed is halved, it takes a −2 penalty to AC and Dexterity saving throws, and it can't use reactions. On its turn, it can use either an action or a bonus action, not both. Regardless of the creature's abilities or magic items, it can't make more than one melee or ranged attack during its turn.

If the creature attempts to cast a spell with a casting time of 1 action, roll a d20. On an 11 or higher, the spell doesn't take effect until the creature's next turn, and the creature must use its action on that turn to complete the spell. If it can't, the spell is wasted.

A creature affected by this spell makes another Wisdom saving throw at the end of each of its turns. On a successful save, the effect ends for it.

A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. Once a creature successfully saves they cannot be affected again for the next 24 hours.

Change Shape. The dragon magically polymorphs into a humanoid or beast that has a challenge rating no higher than its own, or back into its true form. It reverts to its true form if it dies. Any equipment it is wearing or carrying is absorbed or borne by the new form (the dragon's choice).

In a new form, the dragon retains its alignment, hit points, Hit Dice, ability to speak, proficiencies, Legendary Resistance, lair actions, and Intelligence, Wisdom, and Charisma scores, as well as this action. Its statistics and capabilities are otherwise replaced by those of the new form, except any class features or legendary actions of that form.

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.

Tail Attack. The dragon makes a tail attack.

Astral Winds. Any creatures within 10 feet of the dragon must succeed a DC 16 Wisdom saving throw or be thrown back 20 feet, taking 12 (3d6) bludgeoning damage. On a success, any creatures are pushed back 5 feet and take no damage.