Bahamut

Dreadwyrm's Fevor (Recharges after a Short or Long Rest). If the aspect would be reduced to 0 hit points, his current hit point total instead resets to 500 hit points, he charges his Megaflare to 5, and he regains any expended uses of Legendary Resistance. Additionally, the aspect can now use the options in the “Mythic Actions” section for 1 hour. Award a party an additional 155,000 XP (310,000 XP total) for defeating the aspect of Bahamut after his Dreadwyrm's Fevor activates.

Legendary Resistance (5/Day). If the aspect fails a saving throw, he can choose to succeed instead.

Umbral Aura. Bahamut has an aura of magic around him that is 10 ft wide for every charge of Megaflare he currently has. His speed increase by 10 feet for each charge he has, becomes immune to any spell of equal level or lower, and gains a bonus to his saving throws equal to the number of charges

Multiattack. Bahamut makes Two Umbral Strike attacks

Umbral Strikes.  Melee Weapon Attack: +19 to hit, reach 15 ft., one target, to hit, reach 20 ft., one target. Hit: 23 (2d12 + 10) slashing damage plus 22 (4d10) force damage.

Megaflare (Charge 4–6). :Bahamut breathes intense energy from his jaws, blasting all enemies in a 300-ft cone. Each creature in that area must make a DC 27 Dexterity saving throw, taking 162 (25d12) points of force damage on a failed save, or half as much damage on a successful one. This effect ignores evasion.

Change Shape. The aspect magically transforms into any Humanoid or Beast, while retaining his game statistics (other than his size). This transformation ends if the aspect is reduced to 0 hit points or if he uses a bonus action to end it.

Bahamut can take 5 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. Bahamut regains spent legendary actions at the start of his turn.

Attack. The aspect makes one Umbral Strike

Impulse (Recharge 5–6).  Range 120 ft, 4 targets. Hit: (8d10) force damage Bahamut shoots out 4 orbs that attack four different targets within 120 ft of him.

Umbral Frenzy (Recharge 5–6).  Bahamut unleashes a flurry of Umbral Strikes targeting up to 8 creatures. He can move up to half his speed without provoking opportunity attacks. He cannot strike a creature more than once. Melee Weapon Attack: +19 to hit, reach 20 ft., one target. Hit: 23 (2d12 + 10) slashing damage plus 22 (4d10) force damage.

If the aspect’s Platinum Brilliance trait has activated in the last hour, he can use the options below as legendary actions.

Wyrmwave (Recharge 5–6). Bahamut unleashes a pulsing wave from itself in a 40 ft radius. Each creature must make a Strength saving throw or take 66 (12d10) force damage on a failed save.

Deathflare (Recharge 5–6). Bahamat flies into the air and breathes flames in a 50 ft radius around it. Each creature must make a DC 27 Dexterity saving throw or take 25 (8d8) force damage on a failed save and be afflicted with slow. They can make a DC 25 Wisdom save to end the effect at the end of their turn. The entire area become an area with the same effects as silence until Bahamut uses this action again.