Desolate Void:  Any Creature within 40 feet of Almeryctian much succeed on a DC 20 Wisdom  saving throw or  become blind for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to the desolate void for the next 24 hours.

Banishment Immunity: The shadows that whip around Almeryctian prevent banishment, tethering him like anchors to the plain that he chooses to inhabit.

Hell's Offering: Once a creature has been incapacitated Almeryctian can transport them to the fourth circle of hell. This requires Almeryctian to have an undisturbed turn receiving no damage. If successful the creature will be dragged down to hell.

Multi-attack: Almeryctian makes three attacks: one with its bite and two with its claws.

Bite: Melee Weapon Attack: +18 to hit, reach 15 ft., one target. Hit: 22 (2d10 + 10) piercing damage plus 14 (4d6) Acid damage.

Claws: Melee Weapon Attack: +17 to hit, reach 10 ft., one target. Hit: 12 (2d6 + 10) slashing damage.

Acid Breath (Recharge 5-6). Almeryctian exhales acid in a 90-foot cone. Each creature in that area must make a DC 22 Dexterity saving throw, taking 92 (26d6) acid damage on a failed save, or half as much damage on a successful one.

Sinking Shadows: As a reaction Almeryctian can attempt to snare an attacker using tangible darkness. The victim must succeed a DC 18 Dexterity saving throw or be sucked into the ground inflicting D10+8 damage. The creature will remain in the shadowy earth until a saving throw is succeeded, receiving new damage on each failed roll.

Almeryctian 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. Almeryctian regains spent legendary actions at the start of their turn.

Nocturnal Restrain: A shadowy coil can ensnare up to two opponents the creature must make a DC 17 Strength saving throw, or be restrained for the next round.

A Thousand Darkened Blades: Almeryctian can bend the darkness around him into sharpened blades that he can launch at up to three targets inflicting 22 (4d10) damage. (Costs 2 Actions). 

Summon Chain Demon: Almeryctian can summon a chain demon from the pit to serve with him (Recharge 2-3) (Costs 3 actions).