Cul'Tan The Mind Stitcher

Magic Resistance. This creature has advantage on saving throws made against magic effects.

Life Stitching: Cul'tan sends his needle to tear through his foes and connect them with a fate thread. His needle weapon animates and has a fly speed of 20 ft. If a creature is hit with the melee magic weapon attack that Cul'tan makes, the opposing creature must succeed in a DC16 Strength saving throw to stop the needle or be Tethered as the needle passes through your body. A tethered creature cannot move further than 10 feet from an anchor point; if a tethered creature attempts to move further than 10 feet away from this anchor point, they suffer 2d10 Necrotic Damage (Bleeding). After taking this damage, the player can attempt to make a DC 17 Constitution saving throw, if successful, the player is no longer tethered; otherwise, the player remains tethered.

If one tethered creature dies, every tethered creature dies in the same instant. 

(Note that a Dagger of Mind Severing can cut this thread with an attack roll. The Thread's armor class is 5, and its health is 1, but it is entirely immune to all damage aside from damage from this dagger.)

Create Thrall: Target an incapacitated creature grappled by Cul'tan. Melee Weapon Attack +8 to hit 28 (5d10) [Piercing] damage. If this attack reduces the target to 0 hit points, the target becomes a Thrall as the target's brain is implanted with a parasite and is directly placed under the control of Cul'tan through the signal broadcast by the gibbering mouthers placed around the castle.  

Patchwork Man: Certain parts of this creature are sewn onto him, and thus have their own HP. His Wings have 30 HP and are vulnerable to Slashing and cold damage. His Long Tentacle has 40 hp and is vulnerable to slashing damage. Sewn on parts are classified as constructs. 

Innate Spellcasting (Psionics). Cul'tan's innate spell casting ability is Intelligence DC 16
(At will) Detect thoughts

Mind Burst/Blast. (Recharge 5-6) Cul'tan unleashes a burst of magical psionic energy, appearing to other creatures as an invasive and painful mental probe into the front of their skull. Each creature within a 20 foot radius centered on Cul'tan must make a DC 16 Intelligence save or take 22 (4d8+4) [Psychic] damage and be stunned for one minute. A creature stunned by this effect may repeat the saving throw at the beginning of their turn. 

Mind Blast: (Shared Recharge with above) Cul'tan releases a more focused blast of psionic energy, directed in a 60 foot cone in front of him. Everyone within this cone must make an intelligence save or take 31 (5d8+6) be stunned for one minute. The creature may repeat the saving throw at the beginning of their turn. 

Large tentacle: Melee Weapon Attack +8 to hit, reach 15ft, 12 (1d10 +4) [Bludgeoning]. if this attack hits, the target must make a DC 14 Strength Save or be grappled by the tentacle. A creature grappled by the tentacle can be moved up to 10 feet closer to Cul'tan (The large tentacle counts as its own creature (Construct) and has 20 HP vulnerable to slashing damage.)

Multi Attack: this creature makes 2 attacks when it takes this action long tentacle/claw attack, and one needle/claw attack. 

Claw: Melee Weapon Attack +8 to hit 16 (2d6+8) [Slashing] 

Fate Needle. Melee Magic Weapon Attack: +8 to hit, reach 5 ft., 1 target. Hit: 13 (1d8+8) [Piercing] damage. Target is subject to life stitching ability when hit by this weapon.

Extract Brain: Target an incapacitated creature grappled by the Cul'tan. Melee Weapon Attack +8 to hit. 55 (10d10) [piercing] damage. If this target is reduced to 0 hit points by this attack, the target dies as Cul'tan extracts and devours its brain.

Create Thrall: Target an incapacitated creature grappled by Cul'tan. Melee Weapon Attack +8 to hit 28 (5d10) [Piercing]. If this attack reduces the target to 0 hit points, the target becomes a Thrall as the target's brain is implanted with a parasite and is directly placed under the control of Cul'tan through the signal broadcast by the gibbering mouthers placed around the castle.  

Enraged lash. (Reaction to losing the use of an augment) Cul'tan can move up to 15 feet and make a single claw strike at the enemy who removed use of the limb.

This creature can take 2 legendary actions per round at the end of an opponents turn

Large tentacle (1 action): Melee Weapon Attack +8 to hit, reach 15ft, 12 (1d10 +4) [Bludgeoning]. if this attack hits, the target must make a DC 14 Strength Save or be grappled by the tentacle. A creature grappled by the tentacle can be moved up to 10 feet closer to Cul'tan (The large tentacle counts as its own creature (Construct) and has 20 HP vulnerable to slashing damage.)

Wingbeat (1 action): Cul'tan beats his wings, taking flight and rising 5 feet off the ground. His wings look torn and rotting. While his wings are out, he has a fly speed of 30 feet. (the wings count as their own creature (Construct) with 20 HP vulnerable to slashing, piercing, and cold damage. If the wings take cold damage over 10 HP in a single hit, the nerves detach and the wings go limp, dead.)

(Available at 1/4th max HP) Call Thralls (1 action): Vorham sends out a psychic wave of distress through the area accompanied by a terrible screech. Any Enthralled creatures must take the dash action toward the location of Vorham. Upon arrival in combat,  enthralled creatures form a pack and attack as a swarm of average peasants.  Enthralled creatures must protect the Mind Stitcher with their life.