Medium Undead/Aberration, Chaotic Neutral

HP: 175 HP (27d8+54)
AC: 18 (Natural Armor)
Speed: 40 ft.

STR: 14/+2
DEX:22/+6 
CON: 18/+4
INT: 14/+2
WIS: 12/+1
CHA: 12/+1

Saving Throws: Con +9, Wis +6
Skills: Insight +7, Painter’s Supplies +11
Vulnerabilities: Acid, Psychic
Damage Immunities: Poison, Piercing from nonmagical attacks
Damage Resistances: Necrotic, Piercing, Slashing from nonmagical attacks
Condition Immunities: Poisoned
Senses: Blindsight 90 ft., Passive Perception 15
Languages: Common, Deep Speech, Halfling
Challenge: 13
Proficiency Bonus: +5

Haunted Artist. The Künstler is an unstable and unhinged being – haunted by nightmarish visions. His psyche is under the endless assault of great old otherwordly entities, the only things helping him retain his sanity are peaceful solace and painting.
Any creature that deals Psychic damage to the Künstler or attempts to read his thoughts will immediately take 15 (3d10) Psychic damage and make the Künstler hostile and unable to control himself.
Künstler is considered an Undead while sane and an Aberration while succumbing to madness. 

Eldritch Resistance (3/day). If the Künstler fails an Intelligence, Wisdom or Charisma saving throw, he can decide to succeed instead. When this feature is used, the Kunstler takes 15 (3d10) Psychic damage and all creatures within 60 feet of him must make a DC 19 Wisdom saving throw, taking 15 (3d10) Psychic damage on a failure, or half as much on a success. 

Inky Tendrils. As a bonus action or as a reaction upon being hit, the Künstler can take 1d8 Psychic damage and summon a tendril made of ink within 15 feet of himself. The Inky Tendrils have AC 14, 25 Hit Points, are immune to all conditions, cannot move or be moved, and have a +0 bonus to all saving throws.
Each time the Künstler makes the Brush Stroke attack, all Inky Tendrils can make the attack as well, using the same modifiers as the Künstler. Inky Tendrils remain until they are destroyed, or as long as Künstler is in a state of madness or as long as Künstler is aware of any hostile creatures nearby. 

Ink Splotch. As a bonus action, The Künstler can choose an Inky Tendril within 90 feet and create the effect of the Black Tentacles (DC 19) centred on the tendril that lasts until the chosen Inky Tendril is destroyed. Any creature that takes damage from this effect is also Covered in Ink. The Inky Tendrils and the Künstler are immune to the effects. 

Covered in Ink. Creatures that are covered in ink have their movement speed halved, cannot gain any benefits from the invisibility condition, and can be targeted by the Erase my Woes action. The effect is lost upon taking fire or acid damage, or if a creature uses their action to remove it.

Actions. 

• Brush Stroke. Melee Spell Attack: +11 to hit, reach 15 ft., one target. Hit: 27 (6d6+6) necrotic damage and the target must make a DC 19 Dexterity saving throw, being Covered in Ink on a failure.
• Sweet Laudanum. The Künstler drinks from his faithful hip flash, destroying all of his summoned Inky Tendrils, regaining 24 (3d10+8) Hit Points for each Inky Tendril destroyed.
• Erase my Woes. The Künstler summons a giant magical eraser and uses it against a single target that is Covered In Ink within 30 ft. The creature must make a DC 19 Dexterity saving throw, taking 105 (10d10+50) force damage on a failure and becoming affected by the effects of the Banishment spell until the Künstler is incapacitated or until he becomes sane and non-hostile. On a success, the creature takes only half the amount of damage and isn’t banished.