Valak Demon

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

Magic Resistance. The valak demon has advantage on saving throws against spells and other magical effects.

Stench. Any creature that starts its turn within 10 feet of the valak demon must succeed on a DC 14 Constitution saving throw or be poisoned until the start of its next turn. On a successful saving throw, the creature is immune to the valak demon's stench for 24 hours.

Ethereal Sight. The valak demon can see 60 feet into the Ethereal Plane when it is on the Material Plane, and vice versa.

Incorporeal Movement. The valak demon can move through other creatures and objects as if they were difficult terrain. It takes 5 (1d10) force damage if it ends its turn inside an object.

Multiattack. The valak demon makes three attacks: one with its bite and two with its claws.

Bite. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 15 (2d10 + 4) piercing damage.

Claw. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 11 (2d6 + 4) slashing damage.

Etherealness. The valak demon enters the Ethereal Plane from the Material Plane, or vice versa. It is visible on the Material Plane while it is in the Border Ethereal, and vice versa, yet it can't affect or be affected by anything on the other plane.

Possession (Recharge 6). One humanoid that the valak demon can see within 5 feet of it must succeed on a DC 13 Charisma saving throw or be possessed by the valak demon; the valak demon then disappears, and the target is incapacitated and loses control of its body. The valak demon now controls the body but doesn't deprive the target of awareness. The valak demon can't be targeted by any attack, spell, or other effect, except ones that turn undead, and it retains its alignment, Intelligence, Wisdom, Charisma, and immunity to being charmed and frightened. It otherwise uses the possessed target's statistics, but doesn't gain access to the target's knowledge, class features, or proficiencies.

The possession lasts until the body drops to 0 hit points, the valak demon ends it as a bonus action, or the valak demon is turned or forced out by an effect like the dispel evil and good spell. When the possession ends, the valak demon reappears in an unoccupied space within 5 feet of the body. The target is immune to this valak demon's Possession for 24 hours after succeeding on the saving throw or after the possession ends.

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

Telekinetic Thrust (Costs 2 Actions). The valak demon targets a creature or unattended object within 30 feet of it. A creature must be Medium or smaller to be affected by this magic, and an object can weigh up to 150 pounds.
If the target is a creature, the valak demon makes a Charisma check contested by the target's Strength check. If the valak demon wins the contest, the valak demon hurls the target up to 30 feet in any direction, including upward. If the target then comes into contact with a hard surface or heavy object, the target takes 8 (2d6) damage per 10 feet moved.
If the target is an object that isn't being worn or carried, the valak demon hurls it up to 30 feet in any direction. The valak demon can use the object as a ranged weapon, attacking one creature along the object's path (+4 to hit) and dealing 12 (4d4) bludgeoning damage on a hit.

Move. The valak demon moves up to its speed.