Legendary Resistance (4/Day). If Velgaia fails a saving throw, he can choose to succeed instead.

Universal Sense. Velgaia can sense magic as if it was the detect magic spell to a range of 120ft.

Multidimensional Barrier. Veldora is always under the effect of the globe of invulnerability spell except it has a range of touch.

Thought Acceleration. Velgaia has advantage on ability checks and saving throws.

Holy-Demonic Regeneration. At the start of his turn; if Velgaia has at least 1 hit point, he regains 25 hit points unless he was hit by radiant or necrotic damage since his last turn.

Spiritual Attack Nullification. Velgaia is immune to spells and effects that would harm or otherwise change his astral or ethereal body such as cutting his silver cord.

Earthly Rage (Recharges on a short rest). If Velgaia is reduced to 0 hit points, his current hit points become 350 instead, he recharges his breath weapon, and he regains his expended uses of his legendary resistances. Additionally, he can use the options in the "Mythic Actions" Section for 1 hour. 

Multiattack. Velgaia can use its Frightful Presence. It then makes three attacks:

Bite. Melee Weapon Attack: +15 to hit, reach 15 ft., one target. Hit: 19 (2d10 + 8) piercing damage plus 10 (3d6) poison damage.

Claw. Melee Weapon Attack: +15 to hit, reach 10 ft., one target. Hit: 22 (4d6 + 8) slashing damage.

Tail. Melee Weapon Attack: +15 to hit, reach 20 ft., one target. Hit: 17 (2d8 + 8) bludgeoning damage.

Frightful Presence. Each creature of Velgaia's choice that is within 120 feet of him and aware of him must succeed on a DC 19 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 Velgaia's Frightful Presence for the next 24 hours.

All Creation Manifestation. Velgaia uses the effect of the hallucinatory terrain spell except it is not an illusion and any change is physical and permanent unless changed by Velgaia again.

Miasmic Breath (Recharge 5–6). Velgaia exhales poisonous gas in a 90-­-foot cone. Each creature in that area must make a DC 22 Constitution saving throw, taking 77 (22d6) poison damage on a failed save, or half as much damage on a successful one. A creature that fails this save is poisoned for 1 minute.

Spacial Motion. Velgaia teleports to an unoccupied space he can see within 120ft of him.

Universal Shapeshift. Velgaia magically transforms into any creature that is Medium or Small, while retaining his game statistics (other than his size). This transformation ends if Velgaia is reduced to 0 hit points or uses a bonus action to end it.

Velgaia 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. Velgaia regains spent legendary actions at the start of his turn.

Detect. Velgaia makes a Wisdom (Perception) check.

Tail Attack. Velgaia makes a tail attack.

Wing Attack (Costs 2 Actions). Velgaia beats his wings. Each creature within 30 feet of the dragon must succeed on a DC 23 Dexterity saving throw or take 15 (2d6 + 8) bludgeoning damage and be knocked prone. Velgaia can then fly up to half his flying speed.