Belaphoss, Left Hand of Demogorgon

Death Throes. When Belaphoss dies, he explodes, and each creature within a 100-foot-radius sphere centered on him must make a DC 22 Dexterity saving throw, taking 105 (30d6) fire damage on a failed save, or half as much damage on a successful one. The explosion ignites flammable objects in that area that aren’t being worn or carried, and it destroys Belaphoss’s weapons.

Fire Absorption. Whenever Belaphoss is subjected to fire damage from other sources than his own, he takes no damage and instead regains a number of hit points equal to the fire damage dealt.

Fire Aura. At the start of each of Belaphoss’s turns, each creature within 60 feet of him of his choice takes 10 (3d6) fire damage, and flammable objects in the aura that aren’t being worn or carried ignite. A creature that touches Belaphoss or hits him with a melee attack takes 10 (3d6) fire damage.

Flame Mastery. When Belaphoss deals fire damage, he ignores resistance and immunity to such damage. Belaphoss is immune to his own fire damage.

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

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

Magic Weapons. Belaphoss’s weapon attacks are magical.

Multiattack. Belaphoss makes two Greataxe attacks and one Whip attack. He can replace an attack with a use of Spellcasting.

Greataxe. Melee Weapon Attack: +15 to hit, reach 15 ft., one target. Hit: 27 (3d12 + 8) slashing damage, plus 10 (3d6) fire damage. If the target has at least one head and Belaphoss rolled a 20 on the attack roll, the target is decapitated and dies if it can't survive without that head. A target is immune to this effect if it takes none of the damage, has legendary actions, or is Huge or larger. Such a creature takes an extra 27 (6d8) slashing damage from the hit.

Whip. Melee Weapon Attack: +15 to hit, reach 30 ft., one target. Hit: 18 (3d6 + 8) slashing damage plus 10 (3d6) fire damage, and the target must succeed on a DC 23 Strength saving throw or be pulled up to 25 feet towards Belaphoss.

Abyssal Storm (Recharge 5–6). Belaphoss surrounds himself with explosive fire that fills a 60-foot-radius sphere centered on him and spreads around corners. Each creature in the fire must make a DC 22 Dexterity saving throw, taking 28 (8d6) fire damage and 28 (8d6) bludgeoning damage, is pushed 30 feet directly away from Belaphoss, and is knocked prone on a failed save, or half as much damage and is not pushed nor knocked prone on a successful one. Belaphoss is immune to this damage. Objects in the area are subject to it, and the fire ignites flammable objects in the area that aren’t being worn or carried.

Spellcasting. Belaphoss casts one of the following spells, requiring no material components and using Charisma as the spellcasting ability (spell save DC 21):

At will: darkness, detect magic, detect thoughts, fireball, major image

3/day each: banishment, dispel magic, fire storm, mirror image, mislead, polymorph, scrying (as an action), telekinesis, wall of fire

1/day each: dominate monster, power word stun, teleport, time stop

Summon Demons (1/Day). Belaphoss summons one of the following demons: 1d6 vrocks, 1d4 hezrous, 1d3 glabrezus, 1d2 nalfeshnees, one marilith or goristro. A summoned demon appears in an unoccupied space within 60 feet of Belaphoss, acts as an ally of Belaphoss, and can't summon other demons. It remains for 1 minute, until it or Belaphoss dies, or until Belaphoss dismisses it as an action.

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

Change Shape. Belaphoss magically transforms into any Humanoid, Devil or Beast, while retaining his game statistics (other than his size). This transformation ends if Belaphoss is reduced to 0 hit points or if he uses a bonus action to end it.

Belaphoss can take 3 legendary actions, choosing from the options below. Only one legendary action can be used at a time and only at the end of another creature's turn. Belaphoss regains spent legendary actions at the start of his turn.

Abyssal Magic. Belaphoss uses Spellcasting or Teleport.

Whip Strike. Belaphoss makes a Whip attack.

Flaming Pillars (Costs 2 Actions). Belaphoss creates up to four 10-foot-radius, 30-foot-high cilynders of abyssal fire centered on four different points he can see within 150 feet of him. A creature can only be affected by one pillar. Each creature inside the areas of the pillars, must make a DC 22 Dexterity saving throw, taking 28 (8d6) fire damage on a failed save, or half as much on a successful one.

Frightful Presence (Costs 2 Actions). Each creature of Belaphoss choice that is within 120 feet of him and is aware of him must succeed on a DC 21 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 Bephaloss's Frightful Presence for the next 24 hours.