Akmenos of Asmodeus, leader of the Nine Circles

Infernal Legacy. Akmenos has resistance to fire damage. His infernal constitution grants him also resistance to cold and poison damage. He also knows the thaumaturgy cantrip and can cast hellish rebuke as a 2nd-level spell and darkness once per day. Charisma is his spellcasting ability for these spells.

Demands of Nessus. At the start of each of this creature's turns, this creature can choose one ally it can see within 30 feet ofit. The chosen ally loses 10 hit points, and this creature regains the same number of hit points. If the creature is incapacitated, it makes no choice; instead, the closest ally within 30 feet is the chosen ally.

Sneak Attack. Once per turn, Akmenos deals an extra 7d6 damage to one creature he hits with an attack if he has advantage on the attack roll. The attack must use a finesse or a ranged weapon. He doesn’t need advantage on the attack roll if another enemy of the target is within 5 feet of it, that enemy isn’t incapacitated, and he doesn’t have disadvantage on the attack roll.

Evasion. When subjected to an effect that allows him to make a Dexterity saving throw to take only half damage, Akmenos takes instead no damage if he succeeds on the saving throw, and only half damage if he fails.

Blindsense. If Akmenos is able to hear, he is aware of the location of any hidden or invisible creature within 10 feet of him.

Magical Ambush. If Akmenos is hidden from a creature when he casts a spell on it, the creature has disadvantage on any saving throw it makes against the spell this turn.

Spellcasting. Akmenos is a 14th-level Arcane Trickster. Its spellcasting ability is Intelligence (spell save DC 17, +9 to hit with spell attacks). He has the following wizard spells prepared :

At will : friends, mage hand, message, prestidigitation, thaumaturgy (Infernal Legacy)
1st level (4 slots): charm person, ice knife, sleep, Tasha's hideous laughter
2nd level (3 slots): crown of madness, hold person, shadow blade
3rd level (2 slots): fear, phantom steed, vampiric touch
1/day each : hellish rebuke (level 2) and darkness

Multiattack. Akmenos makes three rapier attacks.

Rapier. Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 19 (3d8+5) piercing damage.

Cunning Action. Akmenos can take a bonus action on each of his turns to Dash, Disengage, or Hide.

Versatile Trickster. Akmenos can distract targets with his mage hand. As a bonus action on his turn, he can designate a creature within 5 feet of the spectral hand created by the spell. Doing so gives him advantage on attack rolls against that creature until the end of the turn.

Parry. Akmenos adds 5 to its AC against one melee attack that would hit it. To do so, he must see the attacker and be wielding a melee weapon.

Uncanny Dodge. When an attacker that Akmenos can see hits him with an attack, he can use his reaction to halve the attack’s damage.