Charlotte Iridescent

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

Light Immunity.  Charlotte is immune to light-based spells and effects such as prismatic spray spell or another prismatic's Breath Weapon.

Unusual Nature. Charlotte doesn’t need to eat, drink, sleep, or breathe. She does not age and cannot be aged magically.

Prismatic Awakening (Recharges after a Short or Long Rest). If Charlotte would be reduced to 0 hit points, her current hit point total instead resets to 550 hit points, she recharges her Breath Weapon, and she regains any expended uses of Legendary Resistance. Additionally, Charlotte can now use the options in the “Mythic Actions” section for 1 hour.

Innate Spellcasting. Charlotte casts one of the following spells, requiring no spell components and using Charisma as the spellcasting ability (spell save DC 27, +19 to hit with spell attack):

at will: dancing lights, light, faerie fire, daylight, sunbeam

1/day each: prismatic spray, sunburst, prismatic wall

Multiattack. Charlotte makes one Bite attack, one Claw attack, and one Tail attack. Alternately, she can make three Crystal Blade attacks. 

Crystal Blade (Longsword; Humanoid Form Only). Melee Weapon Attack: +19 to hit, reach 5 ft., one target. Hit: 26 (4d8 + 10) slashing damage plus 16 (4d8) radiant damage.

Bite. Melee Weapon Attack: +22 to hit, reach 25 ft., one target. Hit: 43 (6d10 + 10) piercing damage plus 28 (8d6) force damage.

Claw. Melee Weapon Attack: +22 to hit, reach 20 ft., one target. Hit: 31 (6d6 + 10) slashing damage.  If the target is a creature, it is grappled (escape DC 20). Until this grapple ends, the target is restrained, and the dragon can't bite another target.

Tail. Melee Weapon Attack: +22 to hit, reach 30 ft., one target. Hit: 37 (6d8 + 10) bludgeoning damage, and the target must succeed on a DC 30 Strength saving throw or be knocked prone.

Prismatic Breath (Recharge 5-6). Charlotte exhales prismatic energy in a 300-foot cone, which manifests as eight multicolored rays of light. Each creature in that area must make a DC 26 Dexterity saving throw. On a failed save, the creature takes 71 (11d12) damage of a type chosen by Charlotte: acid, cold, fire, lightning, or poison. On a successful save, the creature takes half as much damage.

Teleport. Charlotte teleports to an unoccupied space she can see within 60 feet of her.

Change Shape. Charlotte magically transforms into any creature that is Medium or Small, while retaining her game statistics (other than her size). This transformation ends if Charlotte is reduced to 0 hit points or uses a bonus action to end it.

Bloodied Breath. When Charlotte falls below half her hit point maximum, she uses her prismatic breath. Charlotte does not need to have her Prismatic Breath charged, and using her breath in this manner does not consume its charge. Once Charlotte uses this reaction, she can't use it again until she reaches her hit point maximum.

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

Attack. Charlotte makes one Claw or Tail attack or she makes an attack with her Crystal Blade.

Wing Attack (Costs 2 Actions). Charlotte 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. Charlotte can then fly up to half her flying speed.

Brilliant Breath (Costs 2 Actions). Charlotte emits a beam of brilliant light flashing out in a 10-foot-wide, 90-foot-long line. Each creature in the line must make a DC 18 Constitution saving throw. On a failed save, a creature takes 24 (6d8) radiant damage and is blinded until the start of Charlotte's next turn. On a successful save, it takes half as much damage and isn't blinded.

If Charlotte’s Prismatic Awakening trait has activated in the last hour, she can use the options below as legendary actions.

Bite. Charlotte makes one Bite attack.

Petrifying Breath (Costs 3 Actions). Charlotte emits a 60-foot cone of petrifying gas from her mouth. Each creature in that area must succeed on a DC 15 Constitution saving throw or take 35 (10d6) poison damage and be restrained as it begins to turn to stone. The restrained target must repeat the saving throw at the end of its next turn. On a successful save, the effect ends on the target. On a failed save, the target is petrified.

Banishing Breath (Costs 3 Actions).  Charlotte emits a 60-foot cone of planar energy from her mouth. Each creature of the dragon's choice in that cone must make a DC 18 Wisdom save or be blinded. It must then remake the Wisdom saving throw at the start of Charlotte's next turn. A successful save ends the blindness. If it fails the save, the creature is transported to another plane of existence of the DM's choosing and is no longer blinded. (Typically, a creature that is on a plane that isn't its home plane is banished home, while other creatures are usually cast into the Astral or Ethereal planes.)