Bolseir, Aspect of Resentment

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

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

Shape changer. Can change shape as an action, equivalent to disguise self. Can hide itself as a normal humanoid of 6ft tall.

Lord of the Dead. Any dead humanoid body can be reanimated by this devil and used to fight on his behalf.

Multiattack. The devil makes three attacks: two with its claws and one with its sting.

Claw. Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 8 (1d8 + 4) slashing damage.

Sting. Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 13 (2d8 + 4) piercing damage plus 17 (5d6) poison damage, and the target must succeed on a DC 14 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.

Innate Spellcasting. The warlock’s innate spellcasting ability is Charisma (spell save DC 14, +6 to hit with spell attacks). It can innately cast the following spells, requiring no material components:

At will: eldritch blast (see “Actions” below), minor illusion

1/day each: armor of Agathys, arms of Hadar, counterspell, crown of madness, invisibility, hunger of Hadar.

Legendary Actions, Has 1/round.

Legendary Resistance, Has 4/short rest. Recharging on a short rest or every 10 rounds. Can use it's legendary resistance to remove a curse or magical effect with a high enough saving throw.