Arigoth, Sorcerer Supreme

Levitation. Arigoth, Sorcerer Supreme levitates 3 feet off the ground and can move freely while levitating. 

Regeneration. Arigoth, Sorcerer Supreme regenerates 30 hit points at the start of his turn.

Sorcerer Points. Arigoth, Sorcerer Supreme has 20 sorcery points. Sorcery points can be used to regain spell slots by using a bonus action.   

Soul Devoured. When Arigoth, Sorcerer Supreme kills an enemy he can devour its soul and heal himself for 5d12 + 10.

Shadow Walk. When Arigoth is in dim light or darkness, as a bonus action, he can magically teleport up to 120 ft. to an unoccupied space he can see that is also in dim light or darkness.

Legendary Resistance (5/Day). If Arigoth, Sorcerer Supreme fails a saving throw, he can choose to succeed instead.

Limited Magic Immunity. Unless he wishes to be affected, Arigoth, Sorcerer Supreme is immune to spells of 6th level or lower. He has advantage on saving throws against all other spells and magical effects.

Spellcasting. Arigoth, Sorcerer Supreme is a 20th-level spellcaster. Its spellcasting ability is Charisma (spell save DC 26, +20 to hit with spell attacks). Arigoth, Sorcerer Supreme has following Sorcerer spells prepared:

Cantrips (at will): Acid Splash, Chill Touch, Fire Bolt 

1st level (at will): Detect Magic, Ray of Sickness

2nd level (at will): Darkness, Detect Thoughts, Flaming Sphere, Web

3rd level (at will): Dispel Magic, Fireball, Gaseous Form

4th level (at will): Blight, Greater Invisibility, Wall of Fire

5th level (5 slots): Telekinesis

6th level (4 slots): Circle of Death

7th level (4 slots): Finger of Death, Plane Shift, Teleport

8th level (3 slots): Abi-Dalzim's Horrid Wilting, Dominate Monster

9th level (3 slots): Power Word Kill, Psychic Scream

Arigoths Books of Power. Arigoth has nine books that orbit him. Each one has a different effect when he wields them. Arigoth may use a bonus action to cycle through his books and select a new one.

1. Necrotic Texts. When necrotic damage is dealt to a creature targeted by Arigoth, he is healed for half the damage done. This effect does not stack with other abilities that heal Arigoth for his necrotic damage, the stronger effect is used.
2. Book of Warding. This book puts a protective barrier around Arigoth, Sorcerer Supreme. Bonus to AC by 1 and Arigoth can deflect up to 3 damage from each attack.
3. Vile Tome. Arigoth, Sorcerer Supreme is surrounded by four tentacles that fight for him. The tentacles sprout from the ground, encompass a 5 ft. square, and appear in the four closest, unoccupied spaces to Arigoth. These tentacles last until a new book is chosen or they are killed. Each tentacle has 30 hit points and an AC of 12.
4. Diary of the Gorgons. This book increases passive perception by 10, grants Truesight for 120 ft., and if a creature is seen while invisible the invisibility is dispelled and they are cursed for 1 minute. A cursed creature will be forced to make a Wisdom saving throw, determined by Arigoth's spell save DC, if it attempts to go invisible again. On a failed saving throw the creature is petrified.
5. Book of Life. Grants the ability to raise the dead. Can be used to create six skeletons as a bonus action. If used to resurrect a creature the book is destroyed. Can pull someones soul back from even the gods and the World Tree.
6. Book of Death. Arigoth can consume the life force of any skeleton he sees and regains hit points equal to their current hit points. If a target within 30 ft. of Arigoth succeeds on a Death Saving throw, he can force that target to re-roll.
7. Elemental Tome. Each spell Arigoth casts does an additional 1d10 damage of its type.
8. Book of Rejuvenation. Arigoth can use an action to regain 3 sorcery points and 4d8+5 health.
9. Book of the Leviathans. This book is Arigoth's last resort, when he uses it he regains all his hit points, Mind Break charges, and sorcery points. This book may only be used if Arigoth has a phylactery on the same plane as him. The phylactery is destroyed when the Book of the Leviathans is used.

Multiattack. Arigoth, Sorcerer Supreme can perform Siphon Souls and 2 Touch of Death attacks per turn. If Arigoth has is wielding the Vile Tomb he may perform a Vile Strike attack instead of one Touch of Death attack.

Touch of Death. Melee Weapon Attack: +12 to hit, reach 5 ft., 1 target. Hit: 17 (3d8 + 5) Necrotic damage plus 12 (3d8) Cold damage. 

Siphon Souls. Arigoth, Sorcerer Supreme can cause hands made of necrotic magic to emerge from the ground in a 30 ft. radius. Each creature in the area of effect must make a Constitution Saving Throw (CON DC 26). On a failed save the creature takes 3d12 necrotic damage. Half as much on a successful save. Arigoth, Sorcerer Supreme regains hit points equal to the total damage done. Hit points lost in this way cannot be regenerated.

Vile Strike. If Arigoth, Sorcerer Supreme is using the Vile Tome he may attack with all tentacles. These tentacles can target a single target or individual targets. +9 to hit, or +11 if attacking the same target. Each tentacle has a reach of 10 ft and does 1d4+2 piercing damage and 1d4+2 necrotic damage. Arigoth, Sorcerer Supreme is healed for the total amount of necrotic damage done.

Banish to the Abyss (Recharge 5-6). Arigoth may attempt to bind a creature within 30 ft. with his magic necrotic hands (DEX DC 26). If he is successful the creature is thrown into a portal to the Abyssal Plane.

Mind Break. When Arigoth is the target of an attack he may force the target to make a DC 26 Wisdom saving throw or be paralyzed by his magic for 1 minute.

Arigoth, Sorcerer Supreme can use five Legendary Actions per round.

Siphon Souls (Costs 4 Actions). Arigoth, Sorcerer Supreme can use his Siphon Souls action.

Shadow Walk (Costs 3 Actions). Arigoth, Sorcerer Supreme can use Shadow Walk for three Legendary Actions.

Switch Books (Costs 1 Actions). Arigoth, Sorcerer Supreme may use a Legendary Action to change the book he is wielding. 

Cast a Spell (Costs 1 Actions). A spell of 6th spell level or lower can be cast.