Astaroth, The Charred Duke

Demolith Subtype. Astaroth has the "(demolith)" tag, which has no rules of its own, but is a tag that affects him in the same way that it would affect a demon or devil.

Semi-Immortal Nature. Astaroth can't die of old age unless affected by magic of a spell of 6th level or higher and doesn't require food, drink, air, or sleep.

Hellfire Guardian. Whenever Astaroth casts a spell, uses an ability, or makes an attack that hits that deals fire damage while he is in or within 1000 feet of a portal to the Burning Hells, the damage bypasses fire resistance and those with fire immunity take quarter damage instead of no damage.

Blessing of Hatred. All evil-aligned creatures within 120 feet of Astaroth (including Astaroth himself) have advantage on attack rolls against good-aligned creatures. Additionally, if the evil-aligned creature has a special degree of hatred and spite toward the good-aligned creature it is attacking, the evil-aligned also gets a +2 bonus to attack and to damage to its attacks when attacking that specific good-aligned.

Multiattack. Astaroth makes three attacks with his glaive, or two with his glaive and one with his spiked chain if not mounted.

Demonic Glaive. Melee Weapon Attack: +11 to hit, reach 10 ft., one target. Hit: 17 (2d12 + 4) slashing damage + 9 (2d8) fire damage.

Spiked Chain (Only usable when not Mounted). Melee Weapon Attack: +10 to hit, reach 20 ft., one target. Hit: 11 (2d6 + 4) bludgeoning damage + 7 (2d6) piercing damage + 3 (1d6) fire damage and the target must succeed on a DC 17 Strength saving throw or be grappled (escape DC 20) by the chain if it is a Large or smaller creature. While grappled in this way, the target has disadvantage on saving throws against the abilities/attacks/spells of Fiends and takes 2 (1d4) fire damage at the start of each of its turns.

Hellfire Meteors (Recharge 4-6). Astaroth swings his glaive around to cause 1d10+1 10-ft wide spheres of blazing hellfire to crash to the ground at random points he can see within 60 feet of him. All targets in the designated area where a meteor falls must make a DC 20 Dexterity saving throw, taking 24 (7d6) fire damage on a failure, or half as much on a success. After the meteors fall, they leave scorching craters in their wake that are the same width as the meteors themselves that last until the end of Astaroth's next turn. Any creature that starts their turn in the area of one of the craters must succeed on a DC 16 Constitution saving throw or take 2 (1d4) fire damage at the start of each of its turns until the end of the next round.

Innate Spellcasting. Astaroth's spellcasting ability is Charisma (spell save DC 22, +14 to hit with spell attacks.). Astaroth can innately cast the following spells, requiring no material components:

At will: detect magic, chaos bolt, fireball, dust devil, darkness, scorching ray (four rays), create or destroy water (only the "destroy" option)

2/day each: wall of fire, dimension door, hold monster

4/day: summon fiend