Radiant Death and Rebirth (Mythic Trait; Recharges after a Short or Long Rest). If the phoenix is reduced to 0 hit points, it doesn’t die or fall unconscious. Instead it explodes and each creature in 60-foot-radius sphere centered on the phoenix must make a DC 27 Dexterity saving throw, taking 22 (4d10) radiant damage on a failed save, or half as much damage on a successful one. Good-aligned creatures have advantage on this saving throw and take no damage if they succeed. The radiance ignites flammable objects in the area that aren’t being worn or carried.

The explosion destroys the phoenix’s old body and out of the ashes rises its new body, which resembles a wingless Aarakocra. It regains 700 hit points, its size becomes Large instead of Gargantuan, it loses its flying speed, its Armor Class is reduced to 20, and it gains access to its Mythic Actions. After 1 hour it explodes yet again and is reborn into its original body (it does not regain any additional hit points from this second explosion). Defeating the Zenith Phoenix after its Mythic Trait activates counts as defeating two CR 30 creatures for the purposes of EXP.

Radiant Form. The phoenix can move through a space as narrow as 1 inch wide without squeezing.

Any creature that touches the phoenix or hits it with a melee attack while within 5 feet of it takes 5 (1d10) radiant damage. In addition, the phoenix can enter a hostile creature’s space and stop there. The first time it enters a creature’s space on a turn, that creature takes 5 (1d10) radiant damage.

With a touch, the phoenix can also ignite flammable objects that aren’t being worn or carried (no action required).

Aura of Feather Falling. If the phoenix or a friendly creature within 120 feet of it begins falling, the creature falls only 60 feet per round, takes no falling damage, and lands on its feet. This effect is suspended if the phoenix is incapacitated.

Flyby. The phoenix doesn’t provoke opportunity attacks when it flies out of an enemy’s reach.

Illumination. The phoenix sheds bright light in a 60-foot radius and dim light for an additional 60 feet.

Legendary Resistance (3/Day). If the phoenix fails a saving throw, it can choose to succeed instead. Alternatively, it can expend uses of its Legendary Resistance to fuel its Armor of Faith ability (see below).

Magic Weapons. Bludgeoning, piercing, and slashing damage dealt by the phoenix is magical.

Siege Monster. The phoenix deals double damage to objects and structures.

Multiattack. The phoenix uses its Heavenly Birdsong and then makes one Beak attack and one Radiant Talons attack.

Heavenly Birsdong. The phoenix's feathers begin vibrating like instruments and play an awe-inspiring melody. Each good-aligned creature within 120 feet of the phoenix that can hear it (including itself) adds 1d4 to all attack rolls and saving throws it makes until the start of the phoenix's next turn. Each evil-aligned creature within 120 feet of the phoenix that can hear it must make a DC 25 Charisma saving throw. On a failed save, it subtracts 1d4 from all attack rolls and saving throws it makes until the start of the phoenix's next turn. If an evil-aligned creature succeeds on its saving throw, it is immune to this effect for 24 hours.

Beak. Melee Weapon Attack: +16 to hit, reach 15 ft., one target. Hit: 10 (1d6 + 7) piercing damage plus 3 (1d6) radiant damage

Radiant Talons. Melee Weapon Attack: +16 to hit, reach 15 ft., one target. Hit: 16 (2d8 + 7) slashing damage plus 4 (1d8) radiant damage

Armor of Faith (Costs 1 Legendary Resistance). The phoenix summons magical armor that defends itself or a creature of its choice within 60 feet of itself. Until this effect ends, the chosen creature has a +10 bonus to its Armor Class. This effect lasts until the start of the phoenix's next turn or until its concentration is broken.

Discordant Melody. When an evil-aligned creature effected by the phoenix's Heavenly Birdsong succeeds on an attack roll or saving throw, the phoenix can use its reaction to subtract an additional 1d4 from the roll's result, possibly turning it into a failure.

Harmonic Melody. When a good-aligned creature effected by the phoenix's Heavenly Birdsong (including itself) fails an attack roll or saving throw, the phoenix can use its reaction to add an additional 1d4 to the roll's result, possibly turning it into a success.

Parry. If the phoenix would be hit by an attack from a creature it can see, it can use its reaction to add 9 to its AC against the triggering attack, potentially turning it into a miss.

The phoenix 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. The phoenix regains spent legendary actions at the start of its turn.

Move. The phoenix moves up to its speed.

Peck. The phoenix makes one Beak attack.

Feather Circle (Costs 2 Actions). The phoenix conjures a circle of whirling, razor-sharp feathers made of magical energy. The circle appears in a spot the phoenix chooses within 90 feet of itself. The circle is between 60 feet in diameter, 20 feet high, and 5 feet thick. The circle provides three-quarters cover to creatures behind it, and its space is difficult terrain. In a 5 foot radius from the center of the circle, bright sunlight shines. Evil-aligned creatures have disadvantage on all saving throws while within this light.

When the circle first appears, each creature within its area must make a DC 25 Dexterity saving throw. On a failed save, the creature takes 33 (6d10) slashing damage. On a successful save, the creature takes half as much damage. A creature must also make this saving throw the first it enters the circle's space on a turn of the first time the circle enters its space on a turn.

At the start of each of the phoenix's turns, the circle closes in so that its diameter is reduced by 10 feet. The circle remains until its diameter is reduced to 0 feet or until the phoenix uses this legendary action again.

Golden Wings (Costs 2 Actions). The phoenix causes a pair of golden wings to sprout from the back of itself or a creature of its choice within 120 feet of itself. While a creature has these wings, it gains a flying speed of 60 feet if it has none or increases its flying speed by 60 feet if it already has one. While a creature has these wings, it has advantage on attack rolls against fiends, oozes, and undead. These wings remain until the end of the phoenix's next turn.

Swoop (Costs 2 Actions). The phoenix moves up to its speed and makes one Radiant Talons attack.

If the phoenix's mythic trait is active, it can use the options below as legendary actions for one hour after using Radiant Death and Rebirth. After the phoenix uses a mythic action, it cannot use the same mythic again the next time it uses one.

Radiant Beam (Costs 2 Actions). The phoenix conjures a cylinder of bright sunlight at a point it chooses within 60 feet of itself. The cylinder has a 5 foot radius and is 60 feet tall. When the cylinder appears, each creature within it must make a DC 25 Constitution saving throw. On a failed save, a creature takes 27 (6d8) radiant damage and is blinded until the end of the phoenix's next turn. On a successful save, it takes half as much damage and isn't blinded. Undead and oozes have disadvantage on this saving throw. A creature must also make this saving throw the first time it enters the cylinder on a turn. The cylinder remains until the end of the phoenix's next turn.

Radiant Meteors (Costs 2 Actions). The phoenix conjures 6 minute meteors and sends them streaking toward a point or points it chooses within 120 feet of itself. Once a meteor reaches its destination or impacts against a solid surface, the meteor explodes. Each creature within 5 feet of the point where the meteor explodes must make a DC 25 Dexterity saving throw. A creature takes 7 (2d6) bludgeoning damage plus 3 (1d6) radiant damageon a failed save, or half as much damage on a successful one. If a creature is in the area of more than one meteor, it makes a single saving throw, taking full or half damage from all meteors affecting it based on the result.

Radiant Storm (Costs 2 Actions). The phoenix conjures a storm made up of sheets of roaring radiance which appears in a location the phoenix chooses within 150 feet of itself. The area of the storm consists of up to ten 10-foot cubes, which the phoenix can arrange as it wishes. Each cube must have at least one face adjacent to the face of another cube. Each creature in the area must make a DC 25 Dexterity saving throw. It takes 38 (7d10) radiant damage on a failed save, or half as much damage on a successful one.

The radiance damages objects in the area and ignites flammable objects that aren't being worn or carried.