Belial (Lord of Wrath)

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

Abyssal Weapons. The archdevil's weapon attacks are magical and deal an extra 5d8 necrotic damage on a hit (included in the attacks).

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

Legendary Resistance (3/Day). If the archdevil fails a saving throw, it can choose to succeed instead.

Innate Spellcasting. The archdevil's spellcasting ability is Charisma (spell save DC 25). The devil can innately cast the following spells, requiring only verbal components:

Cantrips: Fire Bolt,
At will: Detect Evil and Good, Charm Person, Fireball, Fire Shield, Wall of Fire,
Continual Flame, Flame Blade, Flaming Sphere, Scorching Ray, Dragon’s Stride,
3/day each: Summon Fiend, Investiture of Flame, Delayed Blast Fireball, FireStorm,
1/day each: Incendiary Cloud, Meteor Swarm, Illusory Dragon,

Multiattack. The devil makes two attacks with its weapon.

Sword of Kas: Melee Weapon Attack: +16 to hit, reach 6 ft., one target. Hit: 8 (1d10 + 3) slashing damage plus 22 (5d8) necrotic damage. The Sword of Kas is a magic, sentient longsword that grants a +3 bonus to attack and damage rolls made with it. It scores a critical hit on a roll of 19 or 20, and deals an extra 2d10 slashing damage to undead.
If the sword isn't bathed in blood within 1 minute of being drawn from its scabbard, its wielder must make a DC 15 Charisma saving throw. On a successful save, the wielder takes 3d6 psychic damage. On a failed save, the wielder is dominated by the sword, as if by the Dominate Monster spell, and the sword demands that it be bathed in blood. The spell effect ends when the sword's demand is met.
Spirit of Kas. While the sword is on your person, you add a d10 to your initiative at the start of every combat. In addition, when you use an action to attack with the sword, you can transfer some or all of its attack bonus to your Armor Class instead. The adjusted bonuses remain effective until the start of your next turn.
Spells. While the sword is on your person, you can use an action to cast one of the following spells (save DC 18) from it: Call Lightning, Divine Word, or Finger of Death. Once you use the sword to cast a spell, you can't cast that spell again from it until the next dawn.
Bestow Curse. While attuned to the artifact, you can use an action to cast Bestow Curse as a 3rd-level spell from it. After you cast the spell, roll a d6. On a roll of 1–5, you can’t cast it again until the next dawn.
Strengthened Steel. When you hit with a weapon attack while attuned to the artifact, the target takes an extra 1d10 damage of the weapon’s type.
Rotten Fingers. While attuned to the artifact, you deal 1d6 necrotic damage to any plant you touch that isn’t a creature.
Blood Sacrifice. Before you can become attuned to the artifact, you must kill a creature of your alignment.
Sentience. The Sword of Kas is a sentient chaotic evil weapon with an Intelligence of 15, a Wisdom of 13, and a Charisma of 16. It has hearing and darkvision out to a range of 120 feet.
The weapon communicates telepathically with its wielder and can speak, read, and understand Common.
Personality. The sword's purpose is to bring ruin to Raguel. Killing Raguel's worshipers, destroying the ghost rider's works, and foiling his machinations all help to fulfill Ythis’ goal.
The Sword of Kas also seeks to destroy anyone corrupted by the Eye and Hand of God. The sword's obsession with those artifacts eventually becomes a fixation for its wielder.
Destroying the Sword. A creature attuned to the Eyes of God and without sin can use the Wish property of the eyes to unmake the Sword of Kas. The creature must cast the Wish spell and make a Charisma check contested by the Charisma check of the sword. The sword must be within 30 feet of the creature, or the spell fails. If the sword wins the contest, nothing happens, and the Wish spell is wasted. If the sword loses the contest, it is destroyed.

Trumpet of HailFire: While holding the trumpet, you can use an action to blow the horn once a day to cause a Meteor Swarm.

Shapeshifting. (Great Red Dragon) (Sealed)

The archdevil 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. The archdevil regains spent legendary actions at the start of its turn.

Teleport. The archdevil magically teleports, along with any equipment it is wearing or carrying, up to 120 feet to an unoccupied space it can see.

Blinding Gaze (Costs 3 Actions). The archdevil targets one creature it can see within 30 feet of it. If the target can see it, the target must succeed on a DC 15 Constitution saving throw or be blinded until magic such as the lesser restoration spell removes the blindness.