Arvinador

Chromatic Awakening (Recharges after a Short or Long Rest). If Arvinador would be reduced to 0 hit points, her current hit point total instead resets to 425 hit points, she recharges her Breath Weapon, and he regains any expended uses of Legendary Resistance. Additionally, Arvinador can now use the options in the “Mythic Actions” section for 1 hour.

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

Unusual Nature. Arvinador doesn’t require food or drink.

(3/Rest) Action Surge. Arvinador can take a second action. This feature can only be used once per turn. 

Special Equipment. Sevirax's Greed, Dragon Lord's Ensemble, Crystal Ball of Mind Reading

Multiattack. Arvinador makes one Bite attack and two Claw attacks.

Bite. Melee Weapon Attack: +18 to hit, reach 15 ft., one target. Hit: 21 (2d10 + 10) piercing damage plus 13 (2d12) force damage.

Claw. Melee Weapon Attack: +18 to hit, reach 10 ft., one target. Hit: 19 (2d8 + 10) slashing damage. If the target is a Huge or smaller creature, it is grappled (escape DC 20) and is restrained until this grapple ends. Arvinador can have only one creature grappled this way at a time.

Tail. Melee Weapon Attack: +18 to hit, reach 20 ft., one target. Hit: 19 (2d8 + 10) bludgeoning damage. If the target is a creature, it must succeed on a DC 26 Strength saving throw or be knocked prone.

Breath Weapon (Recharge 5–6). Arvinador exhales a blast of energy in a 300-foot cone. Each creature in that area must make a DC 26 Dexterity saving throw. On a failed save, the creature takes 78 (12d12) fire damage. On a successful save, the creature takes half as much damage.

(1/Rest) Second Wind. Arvinador regains 1d10+20 hit points. 

(1/Rest) Hill Rune. Arvinador can invoke the rune as a bonus action, gaining resistance to bludgeoning, piercing, and slashing damage for 1 minute.

(1/Rest) Cloud Rune. When Arvinador or a creature she can see within 30 feet of her is hit by an attack roll, she can use her reaction to invoke the rune and choose a different creature within 30 feet of her, other than the attacker. The chosen creature becomes the target of the attack, using the same roll. This magic can transfer the attack’s effects regardless of the attack’s range.

(1/Rest) Storm Rune. Arvinador enters a prophetic state for 1 minute or until She's incapacitated. Until the state ends, when she or another creature she can see within 60 feet of her makes an attack roll, a saving throw, or an ability check, she can use her reaction to cause the roll to have advantage or disadvantage. 

Arvinador 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. Arvinador regains spent legendary actions at the start of her turn.

Attack. Arvinador makes one Claw or Tail attack.

Wing Attack. Arvinador beats her wings. Each creature within 30 feet of her must succeed on a DC 26 Dexterity saving throw or take 17 (2d6 + 10) bludgeoning damage and be knocked prone. Arvinador can then fly up to half her flying speed.

Scorching Meteor. (2 Actions). Arvinador creates four meteors of magical force and fire. Each spear hits a creature of Arvinador's choice she can see within 120 feet of her, dealing 12 (1d8 + 8) force damage and 7 (2d8) to its target, then disappears.

If Arvinador's Chromatic Awakening trait has activated in the last hour, she can use the options below as legendary actions.

Bite. Arvinador makes one Bite attack.

Chromatic Flare (Costs 2 Actions). Arvinador flares with elemental energy. Each creature in a 60-foot-radius sphere centered on Arvinador must succeed on a DC 26 Dexterity saving throw or take 22 (5d8) fire damage and 13 (3d8) force damage.