Aura of Light. The area within a 120-foot radius around Bahamut is filled with bright celestial light, which creates the following effects:

• Any darkness, whether magical or nonmagical, is dispelled.
• Creatures of Bahamut's choice within that aura cannot be frightened or charmed.
• Creatures of Bahamut's choice within that aura have resistance to necrotic damage as well as advantage on all saving throws.
• Fiends and undead have disadvantage on all attack rolls against creatures within the aura.

Brilliant Platinum Scales. Any time Bahamut is targeted by a magic missile spell, a line spell, or a spell that requires a ranged attack roll, roll a d6. On a 1 to 5, Bahamut is unaffected. On a 6, Bahamut is unaffected, and the effect is reflected back at the caster as though it originated from Bahamut, turning the caster into the target.

If this happens, in addition to the spell's regular effect, the target must make a DC 27 Constitution saving throw or be blinded until the end of its next turn.

Colossal. Bahamut is immune to forced movement, does not provoke opportunity attacks and cannot make opportunity attacks. 

In addition, whenever Bahamut makes a weapon attack, regardless of whether the attack hits or misses, each creature within 20 feet of the attack's target other than the target or Bahamut himself must succeed on a DC 27 Dexterity saving throw or takes half the attack's damage.

Discorporation. When Bahamut dies, his body is destroyed but his essence travels back to his domain on Mount Celestia, and he is unable to take physical form for a time.

Divine Awareness. Bahamut knows if he hears a lie.

Empowered Attacks. Bahamut's weapon attacks count as magical for the purpose of overcoming resistance and immunity to nonmagical attacks.

Immutable Form. Bahamut is immune to any spell or effect that would alter his form, except for his own Change Shape action.

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

Regeneration. Bahamut regains 50 hit points at the start of his turn. If Bahamut takes necrotic damage, this trait does not function at the start of his next turn. Bahamut only dies if he starts his turn with 0 hit points and does not regenerate.

Spellcasting. Bahamut is a 20th level spellcaster. His spellcasting ability is Charisma (spell save DC 27, +19 to hit with spell attacks). He can cast the following spells, requiring no material components:

• Cantrips (at will): all
• 1st level (at will): bless, guiding bolt, healing word, identify,  shield, searing smite
• 2nd level (at will): aid, misty step, spiritual weapon, warding bond, zone of truth
• 3rd level (at will): blinding smite, crusader's mantle, dispel magic, remove curse, spirit guardians
• 4th level (4 slots): aura of life, aura of purity, banishment, death ward, ice storm
• 5th level (3 slots): banishing smite, circle of power, cone of cold, dispel evil and good, greater restoration
• 6th level (3 slots): disintegrate, Fizban's platinum shield, heal, wall of light
• 7th level (3 slots): divine word, plane shift (self only), regenerate, resurrection
• 8th level (2 slots): control weather, glibness, sunburst
• 9th level (2 slots): gate, mass heal, wish

Treasure Sense. Bahamut knows the location of all magic items and of accumulations of mundane treasure within 5 miles of him.

Multiattack. Bahamut can use his Roar of Justice, and if he was flying at the start of his turn, he can use his Crushing Landing. He then makes two attacks with his claws, one with his tail and one with his bite.

Bite. Melee Weapon Attack: +19 to hit, reach 35 ft., one target. Hit: 36 (4d12 + 10) piercing damage plus  18 (4d8) radiant damage plus 18 (4d8) cold damage and Bahamut can grapple the target as part of that attack.

Claw. Melee Weapon Attack: +19 to hit, reach 40 ft., one target. Hit: 32 (4d10 + 10) slashing damage plus  18 (4d8) radiant damage plus 18 (4d8) cold damage. If the target is a creature, it must succeed on a DC 27 Strength saving throw or be flung up to 3d6 × 10 feet away from Bahamut, landing prone.

Tail.  Melee Weapon Attack: +19 to hit, reach 50 ft., one target. Hit: 36 (4d12 + 10) bludgeoning damage plus  18 (4d8) radiant damage plus 18 (4d8) cold damage and the target must make a DC 27 Strength saving throw or be knocked prone.

Roar of Justice. Bahamut unleashes his mighty roar, causing the earth to shake and unholy creatures to shake in fear, as a wave of radiance and justice washes over the lands. Each creature of Bahamut's choice that is within 300 feet of him and can hear him must succeed on a DC 27 Wisdom saving throw. On a failure, if it is a fiend or undead of a CR of 20 or less, it is destroyed and slain instantly, otherwise it becomes deafened until cured by lesser restoration or similar magic and frightened for 1 minute. While frightened in this way, a creature is paralyzed. A frightened creature can repeat the saving throw, 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 Bahamut's Roar of Justice for the next 24 hours.

Crushing Landing. If Bahamut is flying, he can attempt to land forcefully in a space of his choice, even if that space is occupied by other creatures. When he does so, his movement speed is reduced to 0 until the end of the turn, and each creature in Bahamut's space or within 60 feet of hit, other than Bahamut himself, must make a DC 27 Dexterity saving throw or take 39 (6d12) bludgeoning damage and be knocked prone.

Breath Weapon. Bahamut uses one of the following breath weapons; he cannot use the same breath weapon on two consecutive turns:

• Exalting Winds of Celestia: Bahamut breathes the holy winds that howl around the peak of Mount Celestia in a 300-feet cone. Each creature in that area of Bahamut's choice regains 132 (24d10) hit points, and each creature in that area of Bahamut's choice that has been dead for no longer than 1 hour is restored to life with all its hit points. In addition, each creature in that area of Bahamut's choice is cured of any curse, disease, of poison, blindness, deafness and of exhaustion, and if a creature is prone, it can use its reaction to stand up.
• Wrath of the North Wind. Bahamut breathes the freezing winds of the north in a 300-feet cone. Each creature in that area must make a DC 27 Constitution saving throw, taking 132 (24d10) cold damage on a failed save, or half as much damage on a successful one. In addition, on a failed saving throw, a creature is encased in ice until the end of its next turn or until someone uses an action to break the ice off it. While encased in ice, a creature's movement speed is reduced to 0.
• Vaporizing Storm. Bahamut unleashes mighty gusts of winds from the plane of elemental air in a 300-feet cone. Each creature in that area of Bahamut's choice must make a DC 27 Constitution saving throw. On a failure, it is flung up to 3d6 × 10 feet away, takes 66 (12d10) bludgeoning damage and is transformed into vapor as per the gaseous form spell for 1 minute. On a success, the creature takes half as much damage without any other effects.
  An affected creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Change Shape. Bahamut magically polymorphs into a humanoid or beast that has a challenge rating no higher than his own, or back into his true form. He reverts to his true form if he dies. Any equipment it is wearing or carrying is absorbed or borne by the new form (Bahamut's choice).

In a new form, Bahamut retains his alignment, hit points, Hit Dice, ability to speak, proficiencies, Legendary Resistance, lair actions, and Intelligence, Wisdom, and Charisma scores, as well as this action. His statistics and capabilities are otherwise replaced by those of the new form, except any class features or legendary actions of that form.

Quicken Spell (5/day). Bahamut casts one of his spells of 6th level or lower with a casting time of 1 action.

Radiant Ward. Bahamut calls upon the light of Mount Celestia to protect himself and his comrades. Each creature of Bahamut's choice within his Aura of Light, including himself, gains 55 (10d10) temporary hit points and can end one spell or magical effect of its choice on it.

Divine Denial. When a creature within 300 feet of Bahamut that he can see casts a spell or targets Bahamut with an attack, he can use a reaction to force it to make a DC 27 Wisdom saving throw. On a failure, the spell or attack fails. Creatures immune to the charmed are immune to this effect. Clerics of evil-aligned deities can use their Divine Intervention to prevent Bahamut from using this feature for 24 hours.

Protective Wings. When Bahamut sees a creature within 60 feet of him taking damage from an attack or spell, he can spread out his wings to protect the creature. In this case, that creature takes no damage and Bahamut takes the damage instead.

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.

Detect. Bahamut makes a Wisdom (Perception) check.

Smite. Bahamut makes an attack with his claws.

Wing Attack. Bahamut beats his wings. Each creature within 60 feet of Bahamut must succeed on a DC 27 Dexterity saving throw or take 28 (4d8 + 10) bludgeoning damage and be knocked prone. Bahamut can then fly up to half his flying speed.

Cast a Spell (Costs 2 Actions). Bahamut casts one of his spells of 6th level or lower.

Grandfather's Desire (Costs 2 Actions). Bahamut commands up to seven metallic dragons he can see within 300 feet of him to attack. Each dragon can use its reaction to move up to its speed without provoking opportunity attacks and to make one attack with its bite or claws.

Sword of Judgment (Costs 3 Actions). Bahamut targets one creature of his choice that he can see within 60 feet of him, which must make a DC 27 Charisma saving throw. On a failure, a spectral sword of celestial light forms above that creature. If that creature makes an attack, casts a harmful spell or tells a lie, the sword strikes it, dropping the creature to 0 hit points. The sword disappears after 1 minute or after it stroke the creature.

Pillars of Light (Costs 3 Actions). Bahamut conjures seven enormous pillars of searing celestial light that strike the ground at seven different points he can see within 300 feet of him and then disappear. Each creature in a 20-foot-radius, 500-foot-high cylinder centered on each point must make a a DC 27 Constitution saving throw. On a failure it takes 54 (12d8) radiant damage and is blinded until the end of its next turn. On a success, it takes half as much damage and is not blinded. A creature in the area of more than one pillar is affected only once.