Avatar of the Sightless

Superior Threat. The Avatar acts twice in the initiative round, once at Initiative 20 (winning initiative ties), and again at Initiative 10 (losing initiative ties). His legendary actions only recharge on Initiative 20. 

Sightless Seeing. The Avatar can see through magical darkness, and cannot be blinded. 

Magic Resistance. The Avatar has an advantage on saving throws against spells and other magical effects.

Legendary Resistance (4/Day). If the Avatar fails a saving throw, he can choose to succeed instead.

Cull the Seeing. All creatures within 30 ft. of the Avatar when his hand is unfurled (see Bonus Actions) must make a DC 19 Constitution saving throw at the start of their turn, or take 18 (5d6) radiant damage and become charmed for 1 hour. A willing creature can choose to fail this roll and suffer no additional damage. 

Innate Summoning. After 1d4 days of existing on the Material Plane, the Avatar can summon 1d6 Gibbering Mouthers per day. 

Multiattack. The Avatar makes two Grasp attacks and one Vision Rend attack. Alternatively, he can replace both Grasp attacks or his Vision Rend attack with a use of his Spellcasting. 

Grasp of the Sightless. Melee Weapon Attack: +11 to hit, reach 15 ft., 1 target. Hit: 21 (3d10 + 5) bludgeoning damage. If the attack hits, the target must succeed on a DC 19 Dexterity saving throw or become restrained. A creature, including the restrained creature, can use its action to free the restrained creature by succeeding on a DC 19 Strength check.

Vision Rend. Ranged Spell Attack: +10 to hit, range 40/80 ft., 1 target (that he can see). Hit: 26 (4d10 + 4) radiant damage, and the target must make a DC 19 Constitution saving throw or become blinded until the end of their next turn. 

Gaze from Beyond (Recharge 5-6). The Avatar targets up to four creatures it can see within 60 ft, assailing them with visions from an alien world.  Creatures must make a DC 19 Charisma saving throw or take 12d8 Psychic damage on a failed save or half as much damage on a successful one. Additionally, a creature who fails this roll has its movement speed reduced by half and cannot take reactions. 

Spellcasting. The Avatar casts one of the following spells, requiring no material components and using Charisma as the spellcasting ability (spell save DC 19):
At will: fear, unraveling whisper 
3/day each: scarlet dawn (4th level), dominate person, circle of death, counterspell, buried alive 
1/day each: power word: pain, reality break 

Unfurl Hand. The Avatar can unfurl his hand to utilize its Cull the Seeing trait, or sheath it again. While the hand is unfurled, the Avatar is no longer immune to blinded. 

Cling to Life (1/Day). Upon being brought to 0 hit points, the Avatar can extort its will upon the threads of mortality and reality to bring itself back up to full health. 

The Avatar 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. The Avatar regains spent legendary actions at the start of its turn.

Attack (Costs 1 Action). The Avatar makes one Grasp attack or one Vision Rend attack. 

Steal Knowledge (Costs 1 Action). The Avatar targets a creature within 30 feet, temporarily stealing a fraction of its earthly knowledge. The creature must make a DC 19 Wisdom saving throw or temporarily be unable to add its proficiency bonus to any roll it makes until the end of its next turn.  

Break Sanity (Costs 2 Actions). The Avatar targets a creature within melee range with the mental screams of its loved ones. It must make a DC 19 Charisma saving throw or become stunned until the end of their next turn.