Cosmic Fury Bowser

Legendary Resistance (3/Day). If Bowser fails a saving throw, he can choose to succeed instead.

Multiattack. Bowser dragon can use his Frightful Presence. It then makes three attacks: one with his bite and two with his claws.

Bite. Melee Weapon Attack: +17 to hit, reach 15 ft., one target. Hit: 21 (2d10 + 10) piercing damage plus 14 (4d6) fire damage.

Claw. Melee Weapon Attack: +17 to hit, reach 10 ft., one target. Hit: 17 (2d6 + 10) slashing damage.

Tail. Melee Weapon Attack: +17 to hit, reach 20 ft., one target. Hit: 19 (2d8 + 10) bludgeoning damage.

Frightful Presence. Each creature of Bowser's choice that is within 120 feet of Bowser and aware of it must succeed on a DC 21 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 Bowser's Frightful Presence for the next 24 hours.

Fire Breath (Recharge 5–6). Bowser exhales fire in a 90-foot cone. Each creature in that area must make a DC 24 Dexterity saving throw, taking 91 (26d6) fire damage on a failed save, or half as much damage on a successful one.

Fireball: Bowser casts fireball

Quake the Earth: Earthquake, everyone make a DEX saving throw to stay up

Fury Shell Attack: Bowser curls up into his shell and rolls towards any creature, dealing 1d20 bludgeoning damage, 2d20 if STR saving throw failed

Fury Beam: Bowser shoots a burning beam of fire that deals 2d20 fire damage

Jump: Bowser jumps and uses Quake the Earth when he lands, he can jump up to 120ft

Parry: Bowser can parry any weapon attack with claws

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

Detect. Bowser makes a Wisdom (Perception) check.

Tail Attack. Bowser makes a tail attack.

Wing Attack (Costs 2 Actions). Bowser beats his wings. Each creature within 15 feet of Bowser must succeed on a DC 25 Dexterity saving throw or take 17 (2d6 + 10) bludgeoning damage and be knocked prone.  Bowser can then fly up to half its flying speed.

Bowser can take a mythic action at will.

Fury Spikes: Bowser launches off spikes that, upon landing on a character, deal 5d20 piercing damage, and can be dodged with a DEX saving throw

Fury Stomp: Bowser curls up into his shell and jumps, trying to crush whatever he lands on, dealing fatal damage.  Can be dodged with a DEX saving throw

Fury Lightning: Bowser strikes cosmic lightning everywhere, it deals 3d20 thunder damage, and can be dodged with DEX saving throw