Anachronistic Idol

Self-Sustenant. The creature doesn't require external sustenance of any kind.

Legendary Resistance (9/Day, or 12/Day in Lair). If the serpent fails a saving throw, it can choose to succeed instead.

Ethereal Presence  The creature is considered Incorpeal, and therefore takes no damage from non-magical sources.

Uneasy Presence  Construct creatures have disadvantage attacking this creature. (Hit DC and Damage Rolls)

Spiritual Presence  Spirit-like creatures and possessions of any kind have disadvantage attacking this creature (Hit DC and Damage Rolls)

Multiattack. The Storm casts spells five times.. It can replace one attack with a use of Spellcasting to cast Mind Spike (level 5 version)...

Spellcasting. The serpent casts all of the following spells, requiring no Material components and using Charisma as the spellcasting ability (spell save DC 33):

At Will: Detect Magic, Mind Spike (level 5 version), Hypnotic Pattern, Vampiric Touch, Modify Memory, Lightning Bolt, [Tooltip Not Found], Thunderwave, Shocking Grasp
12/Day Each: Geas, Earthquake, Control Weather, Antimagic Field

7/Day Each: Wish

Legendary Action Uses: 9 (12 in Lair). Immediately after another creature’s turn, the dragon can expend a use to take one of the following actions. The dragon regains all expended uses at the start of each of its turns.

Mind Invasion. The dragon uses Spellcasting to cast Mind Spike (level 5 version)

(Charge 10) Hungry Stars When the Anachronistic Idol is threatened, the sky turns to that of a starry night sky no matter the area nor time, additionally the area becomes cold, requiring those in the area to seek some sort of warmth or take 1d6 Cold damage every round. During this, however, the Anachronistic Idol looks as if it is hiding the very moon behind it. Heavy mist covers the grounds as the stars in the sky seem to occasionally shift revealing their falsehood, seemingly being but tattoos on eyelids made of the very space itself, cleaving the space from its usual nature to open, revealing an eye f blinding white light, swirling rapidly after locking onto a threat (happens every 10 rounds). During this, the user must roll a Wisdom Saving Throw of 33 or be forced to roll 1d10 and multiply it by 1d100 and then take that much damage as the stars' eyes swirl into themselves, temporarily creating an absolute abyss so cosmically distraught that it projects the terror of it's being into the mind of the target, each star dealing one psychic damage to the target. If a target is struck by more than 20 in a round, they gain a single count of exhaustion. If the target is struck by 90 or more, they are Paralyzed. If a target is already Paralyzed when struck by 90 or more, they gain the Incapacitated condition as well. 

Dream-like Sub-Space. The dragon passively has Hallucinatory Terrain cast, having a range of 15 miles. The spell has Wisdom Saving Throw: DC 33, each creature having advantage within 15 miles, and disadvantage within 5 miles. For every round, a user must reroll if they fail their initial roll. If they succeed, they are except from having to roll for 5 rounds. Hallucinatory Terrain

 Death of Uranus   For every 1/12 of Total HP dealt to the Anachronistic Idol, the stack the lightning storm goes up by 1d4, additionally, addionally all air, ground, and water spaces within 15 miles feet become rough terrain, regardless of gear or abilities due to earthquakes, rapid winds, and floods.

Army of Anachronism For every 5 creatures killed a Mind Flayer is spawned, having their sole purpose as protecting the Anachronistic Idol, they have Magical Resistance and are Unaligned.

(When >50% HP) Tears of Time Whenever the Anachronistic Idol rains, the water seems to each shine within them their own rainbow, apon gazing on anything rained on due to the Anachronistic Idol, they cast within them a Hallucinatory Terrain, if the target fails a DC 33 Wisdom Saving Throw, they are put under the effects of the spell while also being put in an illusion within their own head until interrupted by another, forcing the user to dream of a world perfectly fit for their character and all those that they care about, carefully crafted to perfectly befit the target's perception, causing the user to slowly cry as they dream. The user may reroll every round to free themselves. Every 5 rounds, the user's body is forced to age 5 years, their mind taking anything that happens within the dream as irrefutable fact, believing it to be real, and for them to actual have moved 5 years into the future. If a creature reaches the end of their lifespan, they die within the false life in their head, and so do they too in actuality.