Ventilation. The dragon can breathe in any enviornment.

Effortless Travel. The dragon can apply its fly speed to any form of movement ( Burrowing, swimming, or simply walking)

Legendary Resistance (1/Day). If the dragon fails a saving throw, it can choose to succeed instead.

Multiattack. The dragon makes three Rend attacks. It can replace one attack with a use of (A) Spellcasting to cast Guiding Bolt (level 4 version) or (B) Rejuvenating Breath.

Rend. Melee Attack Roll: +17 to hit, reach 15 ft. Hit: 19 (2d8 + 10) Slashing damage plus 10 (2d10) Force damage.

Astral Breath (Recharge 4–6). Dexterity Saving Throw: DC 25, each creature in a 100-foot Cone. Failure: 80 (15d10) Force damage. Success: Half damage.

Spellcasting. The dragon casts one of the following spells, requiring no Material components and using wisdom as the spellcasting ability (spell save DC 24, +16 to hit with spell attacks):

At Will: Detect Magic, Guiding Bolt (level 4 version), Shapechange (Beast or Humanoid form only, no Temporary Hit Points gained from the spell, and no Concentration or Temporary Hit Points required to maintain the spell)
1/Day Each: Heal (level 7 version), Wall of Force, Zone of Truth, Forcecage, Antimagic Field

Rejuvenating Breath (Recharge 4–6). Each creature of the dragon's choice within a 90-foot Cone gain advantage on Wisdom-based D20 Tests and regain 75 (10d12) Hit points.

Teleport. As a bonus action the dragon can teleport to any open square within 120 ft.

Commune with Stars. As a bonus action the dragon can chant to channel energy from the heavens to regain use of 1 used spell for the day.

Force Barrier. As a reaction whenever the dragon is targeted by an attack or spell or subject to a damaging effect, either before or after the roll, it may erect a powerful shield. Any attack made with less than a +2 magic weapon is deflected. Any spell of 5th level or lower is reflected to the caster. Any spell of 6th level or higher, has its damage reduced to half.

Element Eater. As a reaction whenever the dragon is targeted by a damaging spell of fire, cold, or lightning, it may choose to devour the magic, regaining hit points equal to the spells damage.

Legendary Action Uses: 3. Immediately after another creature’s turn, the dragon can expend a use to take one of the following actions. The dragon regains all expended uses at the start of each of its turns.

Banish (Costs 1). Wisdom Saving Throw: DC 22, one creature the dragon can see within 120 feet. Failure: 24 (7d6) Force damage, and the target has the Incapacitated condition and is transported to a harmless demiplane until the start of the dragon’s next turn, at which point it reappears in an unoccupied space of the dragon’s choice within 120 feet of the dragon. Failure or Success: The dragon can’t take this action again until the start of its next turn.

Quick Spell (Costs 2). The dragon uses Spellcasting to cast 1 spell.

Twin Breath (Costs 3). The dragon builds enough mana to unleash both Astral breath and Rejuvenating breath at the same time. The dragon cannot use this ability if it has used either breath weapon this turn and cannot use a breath weapon again until they recharge on the following turns.