Amphibious. The dragon can breathe air and water.

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

Ethereal Sight. The dragon spirit can see 60 feet into the Ethereal
Plane when it is on the Material Plane, and vice versa.

Incorporeal Movement. The dragon spirit can move through other
creatures and objects as if they were difficult terrain. It takes 5
(1d10) force damage if it ends its turn inside an object.

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 plus 7 (2d6) poison 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.

Death Breath (Recharge 5–6). The dragon exhales poisonous gas in a 60-foot cone. Each creature in that area must make a DC 18 Constitution saving throw, taking 56 (16d6) necrotic damage on a failed save, or half as much damage on a successful one.

The dragon spirit 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 spirit 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.

When the dragon spirit is reduced to half hit points, it lets out a frightful roar and gains the following features:

Possession (Recharge 6). Two humanoids that the dragon spirit can see within 5 feet of it must succeed on a DC 13 Charisma saving throw or be possessed by the spirit; the spirit then disappears, and the target is incapacitated and loses control of its body.
The spirit now controls the body but doesn't deprive the target of awareness. The spirit can't be targeted by any attack, spell, or other effect, except ones that turn undead, and it retains its alignment, Intelligence, Wisdom, Charisma, and immunity to
being charmed and frightened . It otherwise uses the possessed target's statistics, but doesn't gain access to the target's knowledge, class features, or proficiencies.
The possession lasts until the body drops to 0 hit points, the dragon spirit ends it as a bonus action, or the ghost is turned or forced out by an effect like the dispel evil and good spell. When the possession ends, the space reappears in an unoccupied space within 10 feet of the body. The target is immune to this dragon's spirit's Possession for 24 hours after succeeding on the saving throw or after the possession ends.

Ethereal Jaunt (Recharge 5-6). The dragon jumps into the Ethereal Plane, seemingly vanishing into thin air. It stays hidden for 1d4 rounds, and then appears and attacks.

Mythic Resistance. The dragon spirit gains resistance to attacks from nonmagical weapons.