Bone Devil Taskmaster

Aura of Tyranny. An ally that is within 30 feet of the devil and can see and hear the devil and has less hit points than the devil has advantage to saving throws against being charmed and frightened, provided that the devil isn't incapacitated.

Devil's Sight. Magical darkness doesn't impede the devil's darkvision.

Innate Spellcasting. The devil's innate spellcasting ability is Charisma (spell save DC 16). The devil can innately cast the following spells, without providing material components:
3/day each: fly, invisibility (self only), major image
1/day: wall of ice

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

Spur Allies. As a bonus action, the devil targets up to two allies within 30 feet that can see and hear the devil and must have less hit points than the devil. The target takes 3  (1d6) damage and uses its reaction to make one melee attack with advantage on the roll.

Multiattack. The devil can use its Frightful Presence. It then makes three attacks: two with its claws and one with its sting.  

Claw. Melee Weapon Attack: +9 to hit, reach 10 ft., one target. Hit: 9 (1d8 + 5) slashing damage.

Sting. Melee Weapon Attack: +9 to hit, reach 10 ft., one target. Hit: 14 (2d8 + 5) piercing damage plus 21 (6d6) poison damage, and the target must succeed on a DC 16 Constitution saving throw or become poisoned for 1 minute. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Frightful Presence. Each creature of the devil's choice that is within 120 feet of the devil and aware of it must succeed on a DC 16 Wisdom saving throw or become frightened 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 devil's Frightful Presence for the next 24 hours.