Need help with my CR30 Statblock!

BIG POST WARNING!!

Hey DMAcademy. It has come to that time in my campaign. After many years of work, and many threads to pull, my party are not many sessions away from finally facing the BBEG! I'm super excited, but also want to make it memorable!

The BBEG is called Gy'fellrix, The Thought That Devours. The campaign is in a homebrew spelljammer setting, and is an Eldritch horror. A creature formed purely from thought, now personified, Gy'fellrix grew anytime a citizen of the universe cursed a god. This thought grew with one purpose. To Kill gods.

What I'm asking: Have I overcooked or undercooked this statblock, any tweaks I can make? I'm rubbish at making sure the wording is in line with standard, but to me this all makes sense.

I've never gotten to this phase with a campaign before, and have ran plenty of stuff that ends at lvl 15, but never made it to magical level 20! really wanting to make a decent challenge!

Statblock below:

Huge Aberration (Eldritch), Chaotic Evil

Armor Class: 22 (Eldritch Carapace)

Hit Points: 666 (24d12 + 360)

Speed: 40 ft., fly 60 ft. (hover)

Stats: 20 (+5) | 18 (+4) | 30 (+10) | 28 (+9) | 25 (+7) | 27 (+8)

Damage Resistances: Psychic, Cold, Fire, Thunder; Bludgeoning, Piercing, and Slashing from nonmagical attacks

Damage Immunities: Necrotic, Force

Condition Immunities: Charmed, Frightened, Exhaustion, Stunned, Prone, Unconscious

Senses: Truesight 120 ft., Blindsight 60 ft., Passive Perception 25

Languages: All, telepathy 500 ft.

Challenge: CR 30 (155,000 XP)

Mythic Trait: Collapse of Faith (1/Day)

When reduced to 0 HP, Gy’fellrix’s form collapses into a Swarm of Thought — reforming with 333 HP and changing form, powers, and lair traits. It immediately gains a new set of actions and abilities (see Mythic Phase).

Absorb Despair

At the start of each of its turns, Gy’fellrix regains 10 HP for each creature within 60 feet that is frightened, charmed, or suffering a level of exhaustion.

Worshippers Wane

Whenever a creature within 120 feet casts a divine spell or invokes a god, that creature must succeed on a DC 22 Wisdom saving throw or lose concentration, and the spell fails. On a success, Gy’fellrix takes 3d10 radiant damage. (Once per player).

Legendary Resistance (3/Day)

If Gy’fellrix fails a saving throw, it can choose to succeed instead.

Multiattack

Gy’fellrix makes three attacks: one with Mind Spear, one with Whisper Lash, and one Devour Thought_(If available). If Devour thought is on recharge, use an additional Mind Spear.

Mind Spear (Melee/Ranged Weapon Attack)

+17 to hit, reach 10 ft. or range 120 ft., one target.

Hit: 26 (4d8 + 8) psychic damage, and the target must succeed on a DC 22 Int save or be Confused (as confusion). Players may re-attempt the save at the end of their next turn.

Whisper Lash (Melee Weapon Attack)

+17 to hit, reach 20 ft., one target.

Hit: 22 (3d10 + 6) psychic damage. Target must make a DC 20 Wisdom save or be Frightened for 1 minute. A frightened target takes 2d10 psychic damage** at the start of each of its turns.

Devour Thought (Recharge 5–6)

Target one creature Gy’fellrix can see within 60 feet. That creature must make a DC 23 Intelligence saving throw. On a failure, they take 55 (10d10) psychic damage and lose one 6th-level spell slot*or a Feature tied to their faith (e.g., Divine Smite, Channel Divinity) for 1 hour. On a success, they take half damage and resist the loss.

Legendary Actions (3/round)

Mindquake (Costs 2): Forces all creatures within 60 ft. to make DC 21 Int saves or take 4d10 psychic and suffer Disadvantage on all spell attacks until the end of their next turn.

Warp Will (Cost 1): Force a Wisdom saving throw (DC 20) from one creature Gy’fellrix can see. On failure, they lose their next reaction and must move 15 ft. in a direction of Gy’fellrix’s choice.

Despair Pulse (Costs 2): One creature currently frightened or charmed by Gy’fellrix must make a DC 21 Con save or gain a level of exhaustion.

MYTHIC PHASE - I wont include this for now, but the Mythic phase is more of a skill challenge than it is a fight. I intended this to be a cinematic style victory and a great roleplaying chance. (I can share this in full if you wanna see!)