Celestia

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

Cosmic Adapt. Celestia doesn't need air, food, or water. 

Multiattack. Celestia makes three attacks: one with its bite and two with its claws.

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

Claw. Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 13 (2d6 + 6) slashing damage.

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

Cosmos Breath. The dragon exhales an icy blast in a 30-foot cone. Each creature in that area must make a DC 18 Constitution saving throw, taking 54 (8d8) cold damage on a failed save, or half as much damage on a successful one. Creatures that fail the saving throw also have their movement halved until the end of their next turn. 

Electromagnetic Breath. The dragon exhales a photonic blast in a 30-foot cone. Each creature in that area must make a DC 18 Constitution saving throw, taking 54 (8d8) force damage on a failed save, or half as much damage on a successful one. Concentration on spells is interrupted if the caster fails the saving throw.