Val Hemmek, The Bloody Nightmare

Blood Aegis. The AC of Val Hemmek includes its Constitution modifier while it isn’t wearing armor or wielding a shield.

Sanguine Sense. Val Hemmek can see any creature that isn’t an Undead or a Construct within 60 feet of itself, even through total cover, heavily obscured areas, invisibility, or any other phenomena that would prevent sight.

Nightmare's Strength. For every nightmare chain attached to Val Hemmek. It gains an additional 20 hit points. The destruction of one of these chains deals 30 force damage to Val Hemmek. Val Hemmek starts off the fight with three of these chains active & he can only ever have three active. The chains each have 45 hit points and an AC of 16.

Magic Resistance. Val Hemmek has advantage on saving throws against spells and other magical effects.

Legendary Resistance (3/Day). If Val Hemmek fails a saving throw, it can choose to succeed instead.

Nightmare's Sight. Magical darkness doesn't impede Val Hemmek's darkvision.

Spellcasting. Val Hemmek is a 12th-level spellcaster. Its spellcasting ability is Intelligence (spell save DC 16, +8 to hit with spell attacks). Val Hemmek has the following Wizard spells prepared:
Cantrips (at will): chill touch, ray of frost, toll the dead, frostbite, mind sliver
1st level (4 slots): cause fear, hideous laughter, witch bolt, magic missile, shield
2nd level (3 slots): blindness/deafness, blur, crown of madness, darkness, hold person
3rd level (3 slots): counterspell, fear, lightning bolt, fireball
4th level (3 slots): blight, dimension door, greater invisibility, storm sphere, phantasmal killer
5th level (2 slots): dominate person, mislead, synaptic static
6th level (1 slots): circle of death, eyebite

Multiattack. Val Hemmek makes two attacks with its Blood Lash or Rend Nightmare.

Blood Lash. Melee Spell Attack: +8 to hit, reach 10 ft., one target. Hit: 21 (3d10 + 5) necrotic damage. If the target is a creature, it can’t regain hit points until the start of the blood mage’s next turn. On a hit the target is grappled unless a DC 16 check is made to break the grapple. 

Rend Nightmare. Ranged Spell Attack: +8 to hit, reach 60ft, two targets. Hit: (2d10 + 5) psychic damage. If the target is a creature, it must make a wisdom saving throw (DC 18) or become confused. A creature can repeat this saving throw at the end of every turn. Val Hemmek can only have three creatures affected by this confusion at once. 

Nightmare Mist [Recharge 5-6]. Val Hemmek exhales mist in a 90-foot cone. Each creature in that area must succeed on a DC 18 Constitution saving throw or fall unconscious for 3 rounds. This effect ends for a creature if the creature takes damage or someone uses an action to wake it.

Nightmare's Cursed Dance. Val Hemmek can use a bonus action to control the movement of one creature that it can see within 30 feet of it. The creature must succeed on a DC15 Charisma saving throw or use its reaction to move up to 30 feet in a direction of Val Hemmek's choice. The target then attacks the closest creature if it can reach. 

Val Hemmek can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. Val Hemmek regains spent legendary actions at the start of its turn.

Nightmare Rend. Val Hemmek uses it's Nightmare Rend attack. 

Create Nightmare Chain (2 Legendary Actions). Val Hemmek creates a nightmare chain attached to it's body. 

Displacement (2 Legendary Actions). Val Hemmek teleports up to 60 feet to an unoccupied space it can see.