Death Throes. When the Tenebrous Demon dies, it implodes, and each creature within 60 feet of it must make a DC 20 Dexterity saving throw, taking 70 (20d6) force damage on a failed save, or half as much damage on a successful one.

Fatal Aura. At the start of each of the Tenebrous Demon's turns, each creature within 5 feet of it takes 10 (3d6) cold damage. A creature that touches the Tenebrous Demon or hits it with a melee attack while within 5 feet of it takes 10 (3d6) cold damage.

Magic Resistance. The Tenebrous Demon has advantage on saving throws against spells and other magical effects.

Magic Weapons. The Tenebrous Demon's weapon attacks are magical.

Shadow Lurker. The Tenebrous Demon is invisible in dim light and darkness.

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

Claw. Melee Weapon Attack: +14 to hit, reach 15 ft., one target. Hit: 21 (3d8 + 8) slashing damage plus 13 (3d8) cold damage. Instead of dealing damage with a claw attack, the demon can choose to grapple the target instead, dealing 13 (3d8) cold damage to the target.

Bite. Melee Weapon Attack: +14 to hit, reach 5 ft., one target. Hit: 21 (3d8 + 8) slashing damage plus 13 (3d8) cold damage. This attack automatically hits a target that is grappled by the Tenebrous Demon. Instead of dealing damage, the Tenebrous Demon can choose to swallow the target. Upon failing a DC 15 Dexterity saving through, they are swallowed. While a creature is swallowed, at the start of each of their turns, the take 13 (3d8) cold damage. This creature cannot escape by nonmagical means or deal damage to the Tenebrous demon until the Tenebrous Demon is reduced to 0 hit points or until the Tenebrous Demon successfully swallows another creature, at which point the newly freed creature appears at a random location within 30 feet of the Tenebrous Demon. 

Gaze. The Tenebrous demon chooses a creature that it can see within 60 feet of itself and forces them to make a DC 17 Charisma saving throw. On a failure, a creature teleports into one of the claws of the demon, where they are now grappled.

Teleport. The Tenebrous Demon magically teleports, along with any equipment it is wearing or carrying, up to 120 feet to an unoccupied space it can see.