Apokalypse the Demon God of Evil

Devil's Sight. Darkness and magic doesn't impede the devil's senses

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

Multiattack. The devil makes two attacks with its chains, (up to 6 with all 4 animated chains).

Burning Chain. Melee Weapon Attack: +8 to hit, 10ft cone. Hit: (2d6 + 4) slashing damage. Additionally on hit target(s) takes 4d6 fire damage and catches fire causing them to take 1d10 burn/fire damage at the start of each of their turns until the fire is doused. Also anything flammable in their inventory is destroyed. The targets are also grappled (escape DC 14). Until this grapple ends, the targets are restrained and take (2d6) piercing damage at the start of each of their turns.

Animate Chains (Recharges after a Short Rest). Up to four chains the devil can see within 60 feet of it magically sprout razor-­edged barbs and animate under the devil's control, provided that the chains aren't being worn or carried.

Each animated chain is an object with AC 20, 20 hit points, resistance to piercing damage, and immunity to psychic and thunder damage. When the devil uses multiattack on its turn, it can use each animated chain to make one additional chain attack. An animated chain can grapple one creature of its own but can't make attacks while grappling. An animated chain reverts to its inanimate state if reduced to 0 hit points or if the controller is incapacitated or dies.

Demonic regeneration. at the end of each of his turns he regains 40 (10d6) health.

Unnerving Mask. When a creature the devil can see starts its turn within 30 feet of the devil, the devil can create the illusion that it looks like one of the creature's departed loved ones or bitter enemies. If the creature can see the devil, it must succeed on a DC 14 Wisdom saving throw or be frightened until the end of its turn.

Lord of the 9 Hells (Costs 3 actions): The floor around Apokalypse erupts with the fires of the nine hells. All creatures within 50 horizontal feet of Apokalypse and within 10 vertical feet of the ground must make a dexterity saving throw, suffering (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 Apokalypse's next turn.

Immortal God: Unkillable, when Apokalypse's Hit points are reduced to 0, he dies temporarily before being resurrected to full health in the deepest pits of the 9 Hells.