Argenti the Scorcher

Flames of the Scorcher (Recharges after a Short or Long Rest). If Argenti would be reduced to 0 hit points, their current hit point total instead resets to 500 hit points, they recharge their Breath Weapon, and they regain any expended uses of Legendary Resistance. Additionally, Argenti can now use the options in the "Mythic Actions" section for 1 hour.

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

Frightful Presence. On their turn, Argenti can force a creature that they can see to make a DC 27 Wisdom saving throw. On a failure, the target is frightened of Argenti for 1 minute. A frightened target can repeat the saving throw at the end of each of its turns. On a successful save, a creature is immune to Argenti's Frightful Presence for 24 hours.

Innate Spellcasting. Argenti can innately cast the following spells, requiring no components and using Charsima as the spellcasting ability:

At will: Ashardalon's Stride

Multiattack. Argenti makes one Bite attack, one Claw attack, and one Tail attack.

Bite. Melee Weapon Attack: +19 to hit, reach 20 ft., one target. Hit: 23 (2d12 + 10) piercing damage plus 11 (2d10) fire damage and 11 (2d10) acid damage.

Claw. Melee Weapon Attack: +19 to hit, reach 15 ft., one target. Hit: 21 (2d10 + 10) slashing damage. If the target is a Huge or smaller creature, it is grappled (escape DC 20) and is restrained until the grapple ends. Argenti can have only one creature grappled this way at a time.

Tail. Melee Weapon Attack: +19 to hit, reach 15 ft., one target. Hit: 23 (2d12 + 10) bludgeoning damage. If the target is a creature, it must succeed on a DC 27 Strength saving throw or be knocked prone.

Breath Weapon (Recharge 5-6). Argenti uses one of the following breath weapons:

Acidic Flames. Argenti exhales purple fire and mist in a 300-foot cone. Each creature in that area must make a DC 27 Dexterity saving throw, taking 39 (6d12) fire damage and 32 (5d12) acid damage on a failed save, or half as much on a successful one.
Scorching Corruption. Argenti exhales a white beam of energy in a 300-foot long line that is 10 feet wide. Every Aberration and Dragon in the line regains 71 (13d10) hit points, while every non-Aberration and non-Dragon in the line must make a DC 26 Dexterity saving throw, taking 35 (6d10) radiant damage plus 35 (6d10) necrotic damage on a failed save, or half as much on a successful one. If a creature is reduced to 0 hit points by this damage, it dies, Argenti regains a number of hit points equal to the damage taken.

Change Shape. Argenti magically transforms into any Dragon, Aberration, or Humanoid, while retaining their game statistics (other than their size). This transformation ends if Argenti is reduced to 0 hit points or if they use a bonus action to end it.

Argenti 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. Argenti regains spent legendary actions at the start of their turn.

Attack. Argenti makes one Claw or Tail attack.

Furious Bite (Costs 2 Actions). Argenti makes one Bite attack. If the attack hits a creature, the target must succeed on a DC 27 Wisdom saving throw or become frightened of Argenti until the end of the target's next turn.

If Argenti's Flames of the Scorcher trait has activated in the last hour, they can use the options below as legendary actions.

Interdimensional Shield (Costs 2 Actions). Argenti manifests a void filled with green stars around themself; they gain 77 temporary hit points until the start of their next turn.

Crystalline Strikers (Costs 3 Actions). Argenti conjures four pink crystals that plummet to the ground at four different points Argenti can see within 150 feet of the Scorcher, exploding with white energy on impact. Each creature in a 20-foot-radius, 100-foot-high cylinder centered on each point must succeed on a DC 27 Dexterity saving throw or take 10 (3d6) radiant damage plus 10 (3d6) necrotic damage and 3 (1d6) fire damage. A creature in the area of more than one explosion is affected only once.

Glimpse of Fate (Costs 2 Actions). Argenti targets a creature they are grappling. The creature must succeed on a DC 25 Charisma saving throw or be banished to a world of the Material Plane that Argenti destroyed, taking 44 (8d10) psychic damage as it realizes what horrible fate awaits it. At the start of Argenti's next turn, the creature reappears in an unoccupied space within 10 feet of them.

Power of the End (Costs 3 Actions). Argenti flares with interdimensional power. Each creature of Argenti's choice in a 60-foot radius sphere centered on the Scorcher must make a DC 27 Dexterity saving throw. On a failed save, a creature takes 39 (6d12) damage of a type chosen by Argenti: acid, fire, psychic, necrotic, or radiant. On a successful save, a creature takes half as much damage.