Aurau, master of magic

Boon of immortality. Aurau is immune to the effects of aging and any effect that would age him.

Spellcasting. Aurau is a 30th-level spellcaster. Its spellcasting ability is intelligence (spell save DC 29 , +21 to hit with spell attacks). Aurau has the following wizard spells prepared:
Cantrips (at will): mage hand, fire bolt, shocking grasp, ray of frost, prestigiditation, green Flame, booming blade, toll the dead, infestation, mind sliver
1st level (10 slots): ice knife, disguise self, tasha's hideous laughter, tasha's caustic brew, charm person, witch bolt, unseen servant, magic missile, mage armor (casts on himself before combat), chromatic orb

2nd Level  (9 slots): agnazzar's scorcher, snilloc's snowball storm, enlarge/reduce, blindness/deafness, misty step, scorching ray, invisibility, tasha's mind whip, cloud of daggers,

3rd level (8 slots): intellect fortress, counterspell, sleet storm, fireball, hypnotic pattern, animate dead, fly, melf's Minute meteor

4th level (8 slots): summon elemental, evard's Black tentacles, polymorph, dimension door, divination, summon greater demon (he knows the demon's true name), mordenkainen's faithful hound, summon construct

5th level (8 slots): bigby's hand, dominate person, geas, danse macabre, wall of force, cloudkill, mislead, scrying

6th level (7 slots): dissintegrate, magic jar, soul cage, mental prison, tenser's Transformation, tasha's otherwordly guise, chain lightning

7th level (7 slots): dream of the blue veil, Power Word pain, simulacrum, delayed blast fireball, etherealness, finger of death, plane shift

8th level (6 slots): antimagic field, mind blank (casts on himself before combat), feeblemind, clone, Abi-dalzim's horrid wilting, maze

9th level (5 slots): wish, Power Word kill, mass polymorph, shapechange, invunerability

10th level (4 slots) ((only used for upcasts))

11th level (2 slots) ((only used for upcasts))

12th level (1 slot) ((only used for upcasts))

magical items. He has a cloak of protection, a bag of devouring, a bag of Holding, a cloak of the archmagi, and his arcane focus is so powerful that he ignores all material components, regardless of if they cost anything.

legendary resistance (5/day). If Aurau fails a saving throw he can choose to suceed instead.

magic resistance. Aurau has advantage on saving throws against magic and magical effects.

innate spellcasting. Aurau's innate spellcasting ability is intelligence (spell save DC 27). It can innately cast a number of spells, requiring no material components.

3/day each: shield, protection from evil and good, detect evil and good

1/day: demiplane, glibness

magic weapons. his weapon attacks are considered magical for overcoming immunities and resistances. and he can also use his intelligence modifier when rolling for damage.

Avoidance. If Aurau is subjected to an effect that allows it to make a saving throw to take only half damage, he instead takes no damage if he suceeds, and only half damage if he fails.

Magical essence (recharges after a short or long rest). If Aurau would be reduced to 0 hit points, his current hit point total instead resets to 200 hit points, he regains all uses of legendary resistance, regains all expended spell slots, and immediatley casts a cantrip, and additionally Aurau can now use the options in the "mythic actions" section for 1 hour. Award a party a additional 155000XP (310000XP total) for defeating Aurau after his magical essence activates.

Multiattack. Aura uses arcane bolt twice, his staff of the magi once, and his shortsword three times.

Staff of the magi. Melee Weapon Attack: +11 to hit, reach 5 ft., 1 target. Hit: 23 (3d8 + 10) bludgeoning damage and a additional 15 (3d10) force damage

Arcane bolt. RangedWeapon Attack: +15 to hit, range 20/500 ft., 1 target. Hit: 19 (3d6 + 10) force damage.

shortsword. melee weapon Attack: +15 to Hit, range 5ft., 1 target. hit: 13 (1d6+10) piercing damage.  

Magic deflection (3/day). If targeted by a spell, Aurau can decrease the DC or increase his AC by 3 depending Wether it's a spell attack or a spell with a DC.

Aurau 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. Aurau regains spent legendary actions at the start of its turn.

Arcane bolt attack. Aurau makes arcane bolt attack.

Cast spell. aurau casts a 1st level spell from its spellcasting trait.

magic entrappement (costs 1 action). Aurau forces a creature it can see to make a DC 27 wisdom saving throw or be trapped in a 15ft wide and 5ft tall cube where it is stuck unless it Repeats the saving throw on their turn or if it teleports out.

Draining blast (costs 3 actions). Aurau forces every creature in a 50ft line to roll a DC 27 dexterity saving throw or take 15(3d10) force damage On a failed save or half as much on a successful one. The target's maximum hit points is permanently reduced by the damage taken.

If Aurau's magical essence trait has activated in the last hour, he can use the options below as legendary actions.

Cloak of stars (Costs 2 Action). Aurau teleports up to 50 ft in any direction and forces a creature within 10 ft of it to suceed on a DC 27 Charisma save or be teleported to a demiplane of unthinkable magical energy causing the creature to take 20(4d10) force damage at the start of the creature's turn. The creature can repeat the save at the start of their turn, freeing themselves on a succees.

Shatter the weave (costs 3 Actions). Aurau blasts Magic energy everywhere in a 40ft circle. Every creature in the radius must suceed on a DC 27 dexterity saving throw or take 30 (6d10) force damage or half as much on a successful save and the creature's in the radius cannot use their movement for 1d4 rounds.This effect hurts Aurau as he requires the weave to stay alive in Such a state, After using this Aurau takes 18 (6d6) force damage.