Akuma

Soul Consumer. Whenever the Akuma receives necrotic damage, instead of taking this damage the Akuma gain that much Hit Points.

Divine Vulnerability. Whenever the Akuma receives radiant damage from magic sources, it takes double that damage. If that damage would reduce the Akuma's Hit points to one, it reduces to zero Hit points instead.

Spellcasting. The Akuma is a 4th-level spellcaster. Its spellcasting ability is Wisdom (spell save DC 16, +6 to hit with spell attacks). The Akuma has following Wizard spells prepared:
Cantrips (at will): Fire Bolt, Ray of Frost, Dancing Lights
2nd level (2 slots): Shadow Blade
3rd level (3 slots): Fireball, Summon Lesser Demons
4th level (4 slots): Black Tentacles, Fire Shield

Soul Gatherer. As an action, the Akuma can choose to open the kimono it is wearing and reveal the demonic, huge mouth that is in its torso, making three dark, spiritual hands stretch out and fly to up to three targets. If the target is a creature, it must make a DC 15 Constitution saving throw, taking 2d12 necrotic damage on a fail and half as much damage on a successful one.

Rapid Claws. Melee Weapon Attack: +9 to hit, reach 5 ft., 1 target. Hit: 19 (2d10 + 9) piercing damage. 

Soul Katana. Melee Weapon Attack: +9 to hit, reach 5 ft., 1 target. Hit: 31 (4d8 + 9) slashing damage. 

Abyssal Staff. Melee Weapon Attack: +9 to hit, reach 5 ft., 1 target. Hit: 13 (1d8 + 9) bludgeoning damage. 

Bite of the Paralising Soul. Whenever the Akuma is hit by a nonmagical attack and the attacker is within 5 feet of it, the monster can try to bite the attacker if that creature is the same size or smaller than the Akuma. The creature must make a DC 16 Dexterity saving throw. On a failed save, the creature takes 19 (2d12) necrotic damage and becomes paralised until that creature's next turn. On a successful one, the creature takes half as much damage and isn't paralised.