Astral Nightmare

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

Incorporeal Movement. The Astral Nightmare 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.

Horrific Animation. When the Astral Nightmare moves into a space occupied by a Large or smaller creature, the Astral Nightmare can vanish into the creature, causing it to make a Charisma saving throw DC 18. On a faillure, the creature become a creature under the Astral Nightmare’s control. The Astral Nightmare uses the creature’s statistics in place of its own. The creature also gains the following traits.

• It becomes a nightmarish version of itself
• Its alignment becomes Chaotic Evil

Turn Immunity. The Astral Nightmare is immune against any effect that turns undead.

Malignant Bite. Melee Weapon Attack: +9 to hit, reach 10 ft., one creature. Hit: 23 (4d8 + 5) necrotic damage. The target must succeed on a DC 18 Constitution saving throw or its hit point maximum is reduced by an amount equal to the damage taken. This reduction lasts until the target finishes a long rest. The target dies if this effect reduces its hit point maximum to 0.

Essence Conversion. The Astral Nightmare makes one bite attack against a Medium or smaller target it is grappling. If the attack hits, the target is also swallowed, and the grapple ends. While swallowed, the target is blinded and restrained, it has total cover against attacks and other effects outside the Astral Nightmare, and it takes 21 (6d6) psychic damage at the start of each of the Astral Nightmare's turns. An Astral Nightmare can have only one creature swallowed at a time.

If the Astral Nightmare takes 30 damage or more on a single turn from the swallowed creature, the Astral Nightmare must succeed on a DC 18 Constitution saving throw at the end of that turn or regurgitate the creature, which falls prone in a space within 10 feet of the Astral Nightmare. If the Astral Nightmare dies, a swallowed creature is no longer restrained by it and can escape from the corpse by using 15 feet of movement, exiting prone.

Indoctrinate Spawn. The Astral Nightmare targets a humanoid it has swallowed that has been dead for no longer than 1 minute. The target's spirit rises as a specter in the space of its corpse or in the nearest unoccupied space. The specter is under the Astral Nightmare's control. The Astral Nightmare can have no more than seven specters under its control at one time.