Celestial Colossus

Cosmic Ascendance (Recharges after a Short or Long Rest). If the colossus would be reduced to 0 hit points, its current hit points instead resent to 215, and it emits a pulse of radiant energy. Each creature within 120 ft. of the colossus must make a DC 24 Constitution saving throw, taking 70 (20d6) radiant damage on a failure, or half as much on a success. Additionally, the colossus can now use the options in the "Mythic Actions" section for 1 hour. Award a party an additional 75,000 XP (150,000 XP total) for defeating the colossus after its Cosmic Ascendance trait activates.

Cosmic Awareness. The colossus cannot be surprised while conscious, and has advantage on saving throws against spells and other magical effects.

Innate Spellcasting. The colossus' innate spellcasting ability is Wisdom (spell save DC 24, +16 to hit with spell attacks). It can innately cast the following spells, requiring no material components:

At Will: Detect Evil and Good, Detect Magic, Detect Thoughts
3/Day Each: Dispel Evil and Good, Plane Shift, Telekinesis
1/Day Each: Astral Projection, Gate

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

Stellar Aura. The colossus emits bright light in a 30 ft. radius and dim light for an additional 30 ft. Any creature of the colossus' choice that starts its turn in this bright light must make a C 24 Wisdom saving throw or have the Blinded condition until the end of its next turn.

Multiattack. The colossus makes two Starlight Fist attacks.

Starlight Fist. Melee Weapon Attack: +18 to hit, reach 20 ft., one target. Hit: 36 (4d12+10) radiant damage.

Cosmic Beam. Ranged Spell Attack: +16 to hit, range 150/600 ft., one target. Hit: 54 (12d8) radiant damage.

Divine Decree (Recharge 4-6). The colossus targets one creature it can see within 60 ft. of it. The target must succeed on a DC 24 Wisdom saving throw or follow a command given by the colossus (as per the Command spell).

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

Detect. The colossus makes a Wisdom (Perception) check.

Teleport (Costs 2 Actions). The colossus magically teleports to an unoccupied space it can see within 120 ft. of itself, along with any equipment it is wearing or carrying.

Blinding Gaze (Costs 3 Actions). The colossus targets one creature t can see within 60 ft. of it. If the target can see the colossus, it must succeed on a DC 24 Constitution saving throw or take 28 (8d6) radiant damage and have the Blinded condition until the end of its next turn.

If the colossus' Cosmic Ascendance trait has activated in the last hour, it can use the options below as legendary actions.

Attack (Costs 2 Actions). The colossus makes one Starlight Fist or Cosmic Beam attack.

Starfall (Costs 3 Actions). The colossus calls down a meteor from the heavens at a point it can see within 120 ft. of it. Each creature within a 20 ft. radius centered on that point must make a DC 24 Dexterity saving throw, taking 45 (10d8) radiant damage on a failure, or half as much damage on a success.