Bahamut

Circle of Justice. When Bahamut rolls for initiative, any allies within 80 feet of Bahamut gain +1 bonus to all checks and attack rolls, and any enemy within that area must succeed a DC 20 Wisdom saving throw or take disadvantage on all checks and attack rolls for 1 minute.

Spellcasting. Bahamut can cast any cleric, paladin, or sorcerer spells of 1st level 5/day each. He can cast any cleric or sorcerer spell of 2th-4th levels 3/day each. He can also cast any cleric spell of 5th or 6th level 1/day.

Limited Magical Immunity. Unless he wants to be affected, Bahamut is immune to all spells of 5th level or lower.

Regeneration. Bahamut regains 20 hit points at the start of his turn as long as he is not unconscious.

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

Multiattack. Bahamut can make 3 melee attacks, or he can use a breath weapon and a tail attack.

Claw. +15 to hit, reach 15 feet., one target. Hit: 38 (10d6 + 8) slashing damage.

Bite. +15 to hit, reach 15 feet., one target. Hit: 100 (10d20) piercing damage.

Tail. +20 to hit, reach 20 feet., one target. Hit: 35 (6d10 + 5) bludgeoning damage.

Cold Breath (recharge 5-6). Bahamut exhales cold in a 120-foot cone. Each of the creatures in that area must make a DC 30 Dexterity saving throw or take 100 (10d20) cold damage on a failed save and half as much on a successful one.

Fire Breath (recharge 5-6). Bahamut exhales fire in a 120-foot cone. Each of the creatures in that area must make a DC 30 Dexterity saving throw or take 80 (8d20) fire damage on a failed save and half as much on a successful one.

Disintegration Breath (recharge 5-6). Bahamut exhales a beam of light that is five feet wide and can be up to 400 feet long. Each creature in that area must make a DC 25 Dexterity saving throw, taking 87 (12d12 + 15) force damage on a failed save and half as much on a successful one.

Lightning Breath (recharge 5-6). Bahamut exhales a line of lighting that is 10 feet wide and up to 400 feet long. Each creature in that line must make a DC 25 Dexterity saving throw or take 90 (9d20) lighting damage on a failed save and half as much on a successful one.

Acid Breath (recharge 5-6). Bahamut exhales acid in a 200-foot line that is 10 feet wide. Each creature in that line must make a DC 25 Dexterity saving throw or take 80 (8d20) acid damage on a failed save and half as much on a successful one.

The Bahamut can take 2 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 Bahamut regains spent legendary actions at the start of its turn.

Dragon Summons (costs 1 action, 5/day). Bahamut summons one adult metallic dragon on an unoccupied space he can see.

Wing Attack (costs 2 actions). Bahamut beats his wings. Each creature within 80 feet of him must succeed a DC 30 Dexterity saving throw or take 120 (12d20) bludgeoning damage and be knocked prone.