Astral Dreadnought Reaver

Antimagic Cone. The astral dreadnought’s opened eye creates an area of antimagic, as in the antimagic field spell, in a 150-foot cone. At the start of each of its turns, the dreadnought decides which way the cone faces. The cone doesn’t function while the dreadnought’s eye is closed or while the dreadnought is blinded.

Astral Entity. The astral dreadnought generally can’t leave the Astral Plane, nor can it be banished or otherwise transported out of the Astral Plane except by an exceptionally powerful entity beyond the scope of known gods.

Demiplanar Donjon. Any creature or object that the astral dreadnought reaver swallows is transported to a demiplane that can be entered by no other means except a wish spell or this creature’s Donjon Visit ability. A creature can leave the demiplane only by using magic that enables planar travel, such as the plane shift spell. The demiplane resembles a cave of viscous yellow goo, hardened to a firm state, roughly 1,000 feet in diameter with a ceiling 100 feet high. Like a stomach, it contains the remains of the reaver’s past meals. The dreadnought can’t be harmed from within the demiplane. If the dreadnought dies, the demiplane disappears, and everything inside it appears around the corpse. The demiplane is otherwise indestructible.

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

Magic Weapons. An astral dreadnought reaver’s weapon attacks are magical.

Sever Soul Binding. If the astral dreadnought reaver scores a critical hit against a creature traveling through any Plane that is not their native Plane, the dreadnought can cut the target’s soul binding instead of dealing damage. This means upon death, they are no longer bound to any entity that has bound their soul via subjugation or willingly trading it. This damns the person's soul to possibly be lost forever.

Multiattack. The astral dreadnought reaver makes three attacks: one with its bite and two with its claws.

Bite. Melee Weapon Attack: +17 to hit, reach 10 ft., one target. Hit: 40 (5d10 + 13) piercing damage. If the target is a creature of Huge size or smaller and this damage reduces it to 0 hit points or it is incapacitated, the astral dreadnought reaver swallows it. The swallowed target, along with everything it is wearing and carrying, appears in an unoccupied space on the floor of the astral dreadnought reaver’s Demiplanar Donjon.

Grab & Pound. Melee Weapon Attack: +16 to hit, reach 20 ft., one target. Hit: 19 (3d6 + 9) slashing damage.

The astral dreadnought reaver can take 3 legendary actions, choosing from the options below. Only one legendary option can be used at a time and only at the end of another creature’s turn. The dreadnought regains spent legendary actions at the start of its turn.

Grab & Pound. The astral dreadnought reaver makes one Grab & Pound attack.

Donjon Visit (Costs 2 Actions). One creature that is Huge or smaller that the astral dreadnought reaver can see within 60 feet of it must succeed on a DC 19 Charisma saving throw or be magically teleported to an unoccupied space on the floor of the astral dreadnought reaver’s Demiplanar Donjon. At the end of the target’s next turn, the target reappears in the space it left or in the nearest unoccupied space if that space is occupied.

Energy Well (Costs 3 Actions). Each creature within 60 feet of the astral dreadnought must make a DC 19 Constitution saving throw, taking 37 (3d20 + 5) psychic damage on a failed save, or half as much damage on a successful one.