Bangalore

Avatar of Sin (Mythic Trait; Recharges after a Short or Long Rest). When Bangalore is reduced to half of his total hit points, he swells with unholy fury, initiative order is reset to his turn and uses his Desolation ability regardless of whether it is recharged or not. Bangalore becomes wreathed in hellfire and the dark energies of Nessus itself begin to flow through him for 10 minutes. In this empowered state, Bangalore gains +2 to his AC, increases his movement by 10 feet. If he finishes a short or long rest, his body recovers and becomes able to use the Avatar of Sin again.

Uncontainable. This creature is immune to hindrances such as Ropes of Entanglement, Webs, and even Dimensional Shackles and Bags of Devouring.

Probing Telepathy. If a creature communicates telepathically with Bangalore, he learns the creature's greatest desires if he can see the creature.

Elemental Absorption. Whenever Bangalore is subjected to acid, cold, fire, and lightning damage, he takes no damage and instead regains a number of hit points equal to the acid, cold, fire, and lightning damage dealt.

Arch Devil. Bangalore doesn’t need air, food, drink, sleep, or similar necessities instead he feeds on the emotions and souls of mortals to fuel his Immense power and immortality.

Soul Bartering. Bangalore can grant any humanoid one wish once per week (using the spell wish) in its lifetime on the condition that the PC is bound to him after death. Bangalore can make minor changes to the wishes if he wants.

Brutal Critical. Bangalore critically hits on a natural 19 or 20, and rolls three additional weapon damage die when determining the extra damage for a critical hit with a melee attack. 

Master of Hellfire. Whenever Bangalore deals fire damage, the effect or attack's damage deals maximum damage. Furthermore, his attacks treat immunity as resistance and would ignore normal resistance as well as turning no resistance into vulnerability. Invulnerable effects are also treated as objects with 1,000 hit points, which cannot benefit from resistances or immunities. However he takes half of the damage immediately.

Devil’s Sight. Magical darkness doesn’t impede Bangalore’s Darkvision.

Fiery Weapons. Bangalore’s weapon attacks are magical. When he hits with any weapon, the weapon deals an extra 36 (8d8) fire damage (included in the weapon attacks below).

Legendary Resistance (3/Day). If Bangalore fails a saving throw, he can choose to succeed instead.

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

Regeneration. Bangalore regains 20 hit points at the start of his turn. If he takes radiant damage, this trait doesn’t function at the start of his next turn. Bangalore dies only if he starts his turn with 0 hit points and doesn’t regenerate.

Soul Corrosion. A creature as a soul that has hp equal to its normal hp if they were to take necrotic damage ignore the normal hp but add it towards the souls count. if the soul loses all its HP have their souls reduced to nothingness and can only be restored via the wish spell.

Multiattack. Bangalore Attacks three times with his Soul Harvester. He can substitute Whip of the Dammed for one Soul Harvester Attack, or all three for a Hellfire breath.

Desolation (Recharge 6). Bangalore releases a wave of hellfire, damaging all creatures within 30 feet of him. The target must succeed on a DC 24 Constitution saving throw or take 44 (8d10) necrotic damage and 80 (8d10) fire damage. Creatures that fail the saving throw have their very souls burned by the flames and take 17 (3d10) necrotic damage and the start of their turn. This damage bypasses any damage immunity or resistance and heals Bangalore for the damage dealt. Creatures that die while afflicted by the soul burn have their souls reduced to nothingness and can only be restored via the wish spell. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. Creatures that succeed on the saving throw take half damage and resist the soul burn.

Hellfire Breath (Recharge 6). Bangalore exhales fire in a 100-foot cone. Each creature in that area must make a DC 24 Dexterity saving throw, taking 156 (26d6) fire damage on a failed save, or half that much damage on a successful one. The hellfire ignores resistances and therefore treats immunity as resistance and no resistance as an vulnerability  granted by armor, race, spells, etc.

Soul Harvester. Melee weapon attack:  +17to hit, reach 10ft., one target. 
Hit: 17 (4d6+9) slashing  damage, plus 64 (8d8) Fire damage. In addition the weapon emits a burst of necrotic energy that deals 10 (3d6) necrotic damage to each creature of his choice within 30 feet of it unless they pass a DC 24 constitution saving throw. This damage bypasses any damage immunity or resistance and heals Bangalore for the damage dealt. Creatures that die while afflicted by the soul burn have their souls reduced to nothingness and can only be restored via the wish spell. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. Creatures that succeed on the saving throw take half damage and resist the soul burn.

Whip of the Dammed. Ranged Weapon Attack: +17 to hit, reach 40ft., one target. Hit: 100 (10d10) Fire damage, plus 18 (2d10+8) necrotic damage, Unless they pass a DC 24 constitution saving throw. This damage bypasses any damage immunity or resistance and heals Bangalore for the damage dealt. Creatures that die while afflicted by the soul burn have their souls reduced to nothingness and can only be restored via the wish spell. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. Creatures that succeed on the saving throw take half damage and resist the soul burn.

Now you see me Now you don't (3/Day). As a bonus action on his turn Bangalore can teleport anywhere within his line of sight or in the nine hells.

Bangalore 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. Bangalore regains spent legendary actions at the start of his turn.

Hellish Burst. Bangalore unleashes hellfire in a 5 foot radius centered on himself. Each creature within range must make a DC 24 Dexterity saving throw, taking 24 (3d8) fire damage and 14 (3d8) necrotic damage on a failed save, or half as much damage on a successful one.

Enflame Soul (Costs 2 Actions). Bangalore turns his magical gaze toward one creature that is currently suffering from soul burn and commands the flame to roar more intensely. The target must succeed on a DC 24 Wisdom saving throw or take 28 (5d10) necrotic damage.

Invoke Asmodeus (Costs 3 actions): The floor around Bangalore erupts with the fires of the nine hells. All creatures within 50 horizontal feet of Bangalore within 10 feet of the ground must make a dexterity saving throw, suffering 120 (12d10) fire damage on a failed save and half as much on a successful one. The ground in this area is considered difficult terrain until the start of Bangalores next turn.

If Bangalores mythic trait is active, he can use the options below as legendary actions for the duration of Avatar of Sin.

Rampage. Bangalore makes an attack with Soul Harvester against every enemy creature within range.

Rage of Nessus (Costs 2 Actions). Each creature within 15 feet of Bangalore must make a DC 24 Dexterity saving throw, taking 22 (5d8) necrotic damage on a failed save, or half as much damage on a successful one.