Asmodeus, The Lord of the Nine Hells

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

Discorporation. When Asmodeus drops to 0 hit points or dies, his body is destroyed but his essence travels back to his domain in the Nine Hells, and he is unable to take physical form for a time.

Innate Spellcasting. Asmodeus's spellcasting ability is Charisma (spell save DC 25). He can cast the following spells, requiring no material components:

At will: alter self, bestow curse

3/day each: banishing smite, dominate person, geas

2/day each: antimagic field, divine word, forbiddance

1/day each: incendiary cloud, imprisonment, prismatic wall

Legendary Resistance (5/Day). If Asmodeus fails a saving throw, he can choose to succeed instead.

Limited Magic Immunity. Unless he wishes to be affected, Asmodeus is immune to spells of 5th level or lower. He has advantage on saving throws against all other spells and magical effects.

Magic Weapons. Asmodeus's weapon attacks are magical.

Regeneration.  Asmodeus regains 30 hit points at the start of his turn.

Prince of Evil. All devils have disadvantage against spells or abilities used by Asmodeus that would command them or affect their minds.

Royal Decree. Asmodeus can cast Command at will, and when he targets devils he can cast it as a 9th level spell. Devils who have sworn fealty to him automatically fail their saving throws.

Ruby Rod of Asmodeus. Asmodeus wields the Ruby Rod, one of the most powerful artifacts ever created. Among other things, it acts as a Rod of Rulership (DC 25). If he strikes a devil with it, the devil must make a DC 25 Constitution saving throw or die instantly. 

Hurl Through Hell: When Asmodeus hits a creature with an attack, it can use this feature to instantly transport the target through the lower planes. The creature disappears and hurtles through a nightmare landscape.

At the end of Asmodeus's next turn, the target returns to the space it previously occupied or the nearest unoccupied space. If the target is not a fiend, it takes 10d10 psychic damage as it reels from its horrific experience.

Once this feature has been used, it cannot be used again until after a long rest.

Multiattack Asmodeus can use his frightful presence. He then makes three attacks: one with the Ruby Rod of Asmodeus, one with an Unarmed Strike and one with the tail.

Ruby Rod of Asmodeus. Melee or Ranged Weapon Attack: +16 to hit, reach 10 ft. or range 150/600, one target. Hit: 39 (7d8 + 7 ) bludgeoning damage.

Hellfire (Recharge 5-6). Asmodeus summons the flame from Phlegethos in a 90-foot cone. Each creature in the area must make a DC 25 Dexterity saving throw, taking 65 (10d12) fire damage on a failed save, or half as much damage on a successful one. 

Hutijin's Lightning Storm (Recharge 5-6). Asmodeus calls upon his rival's servant's power and unleashes lightning from his rod in a 50-foot line that is 5 feet wide, each creature in that line must make a DC 25 Dexterity saving throw, taking 33 (5d12) lightning damage on a failed save, or half as much damage on a successful one.

Mammon's Acid Rain (Recharge 5-6). Asmodeus calls upon the acid rains from Minauros, the third level of the Nine Hells. It is summoned from his rod and is opened in a 30-foot -radius, 60-foot-high cylinder on a point that he can see. Each creature must make a DC 25 Dexterity saving throw, taking 33 (5d12) acid damage on a failed save, or half as much damage on a successful one.

Cania's Icy Hellstorm (Recharge 5-6). Asmodeus siphons power from his rival, Mephistopheles, and creates a cone of icy hell in a 60-foot cone. Each creature must make a DC 25 Dexterity saving throw, taking 33 (5d12) cold damage on a failed save, or half as much damage on a successful one.

Unarmed Strike. Melee Weapon Attack: +16 to hit, reach 5 ft., one target. Hit (5d8 + 7 ) Bludgeoning damage plus (4d6) fire damage.

Tail. Melee Weapon Attack +16 to hit, reach 5 ft., one target.Hit (4d6 + 7) Bludgeoning damage plus (4d6) fire damage

Frightful Presence. Each creature of Asmodeus’s choice that is within 240 feet of Asmodeus and aware of him must succeed on a DC 26 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature’s saving throw is successful or the effect ends for it, the creature is immune to Asmodeus's Frightful Presence for the next 24 hours.

Teleportation. As a bonus action on his turn, Asmodeus can teleport anywhere within his line of sight or in the nine hells.

Asmodeus can take 5 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. Asmodeus regains spent legendary actions at the start of his turn.

Chilling Gaze (Costs 1 Action). Asmodeus targets one creature within 30 ft., the target makes a DC 25 Constitution saving throw or the target takes 2d10 psychic damage. The target also becomes frightened and suffers one level of exhaustion. 

Hell's Gate (Costs 2 Actions). As the Supreme Ruler of the Nine Hells, Asmodeus has absolute control over all of the gates and portals that lead to Hells, as well as those within the Hells. Asmodeus can cause a gate or portal to open, forcing up to 8 creatures within 30 feet of the portal to make a DC 25 Wisdom saving throw or be teleported to a location in the Nine Hells of Asmodeus' choosing. 

Call of the Lord (Costs 2 actions.) Asmodeus can summon three fiends (with a challenge rating of 5 or below) who reside within the Nine Hells.