Huge fiend, monstrosity, any evil alignment

Armor Class: 5

Hit Points: 1(1d12-5) 1d12-5

Speed: 60 ft , climb: 60 ft

STR

1 -5

DEX

1 -5

CON

1 -5

INT

26 +8

WIS

26 +8

CHA

1 -5

Saving Throws: STR -1 1d20-1 , DEX -1 1d20-1 , CON -1 1d20-1 , INT +12 1d20+12 , WIS +12 1d20+12 , CHA -1 1d20-1

Damage Immunities: All when dream walking

Condition Immunities: charmed, frightened, grappled, incapacitated, paralyzed, petrified, poisoned, prone, restrained, stunned, unconscious

Senses: truesight 500 ft., passive Perception 18

Languages: Mimics all languages but only understands Void Speech, telepathy 300ft

Challenge Rating: 10

Proficiency Bonus: 4

Actions

Multiattack: The The Haunting One makes five attacks.
Nightmare Claw: Melee Weapon Attack: -1 to hit, reach 10 ft., one target. Hit: 2 (2d6 - 5) 2d5-5 slashing damage. If The Haunting One is Dream Walking, the attack instead is +12 to hit, reach 10 ft., one target. Hit: 35 (6d8 + 8) 6d8+8 Psychic damage.

Bonus Actions

Mimic: The Haunting One is able to use its host's dreams to alter its appearance to match anyone or anything that the creature would know. It maintains this form until the end of its next turn, unless it uses this ability again.
Marked: The Haunting One can form a psychic link with its host. The Haunting One is then able to use Dream Walker anytime it they sleep or meditate without having to have line of sight. It only loses the link if it uses the ability to link with another target, or its host manages to kill The Haunting One.

Reactions

Reactive: The The Haunting One can take one reaction on every turn in combat.
Dream Walker: When The Haunting One sees a sleeping creature, it can use the Void to drag them into a dream like state. Creatures who do not dream still enter this state. The Haunting One then enters the dream, leaving no physical trace of itself in the material world.
Dream Eater: As a reaction to a creature waking, The Haunting One will unleash all its energy to destroy the dream state, and tear the creatures mind. The sleeping creature must pass a DC 22 INT save. On a pass, nothing happens. On a fail, the creature takes Psychic damage equal to The Haunting One's hp. After the attack, The Haunting One's health drops to 1 and it is brought back to the material world.