Constant Madness. If a creature attempts to enter or influence Caiphon's mind in any way, it has to make a DC 22 Intelligence saving throw and receives 36 (8d8) psychic damage on a failed save. On a success the damage is halved. 

Deep Mind. Caiphon has advantage on Constitution saving throws to maintain Concentration spells. Additionally, he can concentrate on 3 Concentration Spells at once. However, he loses his advantage while maintaining two and has disadvantage while maintaining 3. On a failed save it will lose concentration on all spells.

Discorporation. When Caiphon drops to 0 hit points or dies, his body is destroyed, but his essence travels back to his domain in the Far Realms, and he is unable to take physical form for a time.

Legendary Resistance (5/Day). If Caiphon fails a Saving Throw, he can choose to succeed instead.

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

Magic Weapons. Caiphon’s weapon attacks are magical.

Regeneration. Caiphon regains 30 (10d4+6) Hit Points at the start of his turn.

Multi Attack. Caiphon makes 3 Arcane Blast attacks or 3 Arcane Cudgel attacks, and casts one spell per action.

Arcane Blast. Ranged Spell Attack: +17 to hit, range 120 ft., one target. Caiphon hurls a purple orb of energy toward any point within range. Target takes 32 (4d10 + 10) force damage.

Arcane Cudgel. Melee Weapon Attack: +17 to hit, range 15 ft., one target. Caiphon strikes out with his unholy weapon. Target takes 34 (4d12 + 10) force damage.

Psychic Burst. (Recharge 4-6) Ranged Weapon Attack: +17 to hit. Caiphon sends out damaging psychic waves in a 90 ft. cone. Creatures within it must make a DC 27 Constitution saving throw or take 67 (14d8 + 4) psychic damage and be pushed back 45 ft. On a successful save, the creature takes half damage and is pushed back 20 ft. Creatures who fail the save by 5 or more are frightened of Caiphon for the next minute. Creatures effected can make a Constitution saving throw at the end of their turn to end their condition early.

Spellcasting. Caiphon casts one of the following spells, using Wisdom as it’s spellcasting ability (spell save DC 26)

At will: Blindness/Deafness, Catnap, Counterspell (7th level), Fast Friends, Thaumaturgy, Vortex Warp.

2/day each: Blight, Dissonant Whispers, Evard’s Black Tentacles, Fear, Invisibility, Raulothim’s Psychic Lance, Summon Undead (6th level).

1/day each: Dark Star, Feeblemind, Finger of Death, Globe of Invulnerability, Mental Prison,  Power Word: Pain, Power Word: Stun.

Caiphon has 5 legendary actions per round.

Arcane Cudgel (Costs 1 Action). Caiphon attacks once with Arcane Cudgel.

Arcane Blast (Costs 1 Action). Caiphon attacks once with Arcane Blast.

Necrotic Leech (Costs 3 Actions). Caiphon condenses his magical energy into a controlled void centered on him. Each creature within 25ft. of Caiphon must make a DC 26 Constitution saving throw or take 23 (2d12 + 10) necrotic damage and be pulled 20 ft toward him. Creatures who save take half damage and don’t get moved. Caiphon heals the same amount as damage dealt.

Spellcasting (Costs 2 Actions). Caiphon casts one spell on his list.