Arruluth, Greater Shadow Demon

Incorporeal Movement. The demon can move through other creatures and objects as if they were difficult terrain. It may remain within solid terrain until the beginning of its next turn without penalty but must emerge within 15 feet of where it entered.

Light Sensitivity. While in bright light, the demon has disadvantage on attack rolls, as well as on Wisdom (Perception) checks that rely on sight.

Planar Anchoring. The demon can physically connect with an object, weapon, or item in the possession of a creature with whom it has made a pact. Unless this anchor is destroyed, the pact is not considered dissolved and the demon may return to the creature at any time, hiding within the creature's corporeal form indefinitely.

Pact/Possession. Once a pact has been made, the demon may anchor itself to a belonging of the creature with whom it has the pact. While this pact is active, the creature gains the following benefits: 

• Damage reduction. All Piercing, Slashing, Bludgeoning damage is reduced by 2.
• Darkvision. A creature without Darkvision is granted Darkvision to 15 ft. A creature with Darkvision has their Darkvision extended by an additional 15 ft. (This effect does not stack with other effects that extend Darkvision.)

Shadowy Escape: When the demon is reduced to zero hit points, it becomes a small pile of shadow and attempts to return to its host.

Legendary Resistance (2/Day). If the demon fails a saving throw, it can choose to succeed instead.

Multiattack. The demon makes two claw attacks.

Claws. Melee Weapon Attack: +9 to hit, reach 10 ft., one creature. Hit: 25 (4d6 + 9) psychic damage or, if the demon had advantage on the attack roll, 41 (8d6 + 9) psychic damage.

Suppression (triggers in the course of a multiattack): On a failed saving throw (Wisdom, DC 17), the demon's influence controls the will of the target, dominates the target per the spell.

Rampage Pulse. [Recharge 5-6] A 20-foot-radius of magical confusion spreads outward from the demon and is not blocked by cover. Each creature within the radius must make a Wisdom Save (DC 17) or be forced to attack a random friendly target within range with a melee attack. On a successful save the creature takes 8 (2d6)

Shadow Stealth. While in dim light or darkness, the demon may use the Disengage or Hide action as a bonus action on its turn. 

Shadow Movement. The demon may teleport from one shadow to another shadow within 60 feet without using its movement. 

Mark of Vengeance: The demon casts [Tooltip Not Found] and marks a target, granting it advantage on attacks and an additional 8 (2d6) psychic damage on the marked target. The Mark can be moved to another creature as a bonus action.

Claws. Melee Weapon Attack: +9 to hit, reach 10 ft., one creature. Hit: 25 (4d6 + 9) psychic damage or, if the demon had advantage on the attack roll, 41 (8d6 + 9) psychic damage.

The demon can take 2 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 demon regains spent legendary actions at the start of its turn.

Attack. The demon makes one attack.

Move. The demon moves up to its speed without provoking opportunity attacks.

Psychic Drain (Costs 2 Actions): One creature dominated by the demon takes 8 (2d6) psychic damage, and the demon regains hit points equal to the damage the creature takes.