Demonic Weapons. Zalthor's weapon attacks are magical. When Zalthor hits with any weapon, the weapon deals an extra 27 (6d8) necrotic and 27 (6d8) fire damage (included in the attack).

Paranoia and delusion. Zalthor's grasp of reality is limited and distorted, it has disadvantage against saving throws that cause blindness or deafness. The demon is constantly in doubt about everything, even the simplest of truths.

Punish the Weak. Zalthor deals 4x damage against prone creatures. All the demon's attacks have advantage against creatures that are either prone or smaller than him, and those creatures have disadvantage on saving throws against his attacks. Zalthor has an additional +5 to hit against prone targets.

Takedown. Every time Zalthor makes a melee hit, the target must succeed on a DC 18 (or 20 on a crit) strength saving throw or be knocked prone.

Innate Spellcasting. Zalthor's spellcasting ability is Charisma (spell save DC 24). It can innately cast the following spells, requiring no material components:

At will: detect evil and good, invisibility (self only), firebolt, burning hands, charm person, command, false life, hideous laughter, inflict wounds, shield, sleep, continual flame, darkness

5/day each: blade barrier, dispel evil and good, aganazzar's scorcher, blindness/deafness, flame blade, hold person, ray of enfeeblement, scorching ray

4/day each: bestow curse, fireball, flame arrows, melf's minute meteor, vampiric touch

3/day each: banishment, blight, charm monster, charm monster, dominate beast, fire shield, wall of fire, contagion, dominate person, immolation, modify memory

2/day each: blade barrier, circle of death, delayed blast fireball, firestorm, power word pain, dominate monster, demi plane, maddening darkness, incendiary cloud, power word stun

1/day each: meteor swarm, power word kill, storm of vengeance, time ravage, wish

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

Multiattack. Zalthor makes one greatsword attack or one great axe attack, then makes one deathly longbow attack or one horn attack.

Great axe. Melee Weapon Attack: +12 to hit, reach 5 ft., one target. Hit: 69 (5d20 + 17) slashing, 27 (6d8) necrotic, and 27 (6d8) fire damage. On a crit, the great axe is covered in flames and instead deals 160 (12d20 + 34) slashing, 78 (12d12) necrotic, and 78 (12d12) fire damage to all enemies on a 10 ft. radius.

Greatsword. Melee Weapon Attack: +17 to hit, reach 5 ft., one target. Hit: 82 (10d12 + 17) slashing, 27 (6d8) necrotic, and 27 (6d8) fire damage.

Deathly Longbow. Ranged Weapon Attack: +15 to hit, range 900 ft., one target. Hit: 50 (6d10 + 17) piercing, 27 (6d8) necrotic, and 27 (6d8) fire damage. If the target is a creature that has 100 hit points or fewer, it must succeed on a DC 18 Constitution saving throw or die.

Horn. Melee Weapon Attack. +17 to hit, reach 5 ft., one target. Hit: 44 (6d8 + 17) piercing, 44 (6d8 + 17) bludgeoning, 27 (6d8) necrotic, and 27 (6d8) fire damage. The target must succeed on a DC 22 (or 24 on a crit) strength saving throw or be knocked prone. If the target fails the saving throw, Zalthor makes an extra greatsword attack against the creature.

Flying Sword. Zalthor releases its greatsword to hover magically in an unoccupied space within 5 feet of it. If Zalthor can see the sword, the demon can mentally command it as a bonus action to fly up to 150 feet and either make one attack against a target or return to the solar's hands. If the hovering sword is targeted by any effect, Zalthor is considered to be holding it. The hovering sword falls if the demon dies.

Withering Touch (5/Day). Zalthor touches another creature. The target magically takes 71 (12d8 + 17) necrotic, 71 (12d8 + 17) fire damage, and is cursed (is always prone) until its next long rest.

Hell Breath (3/Day, Recharge 3-4). Zalthor exhales fire in a 120-foot cone. Each creature in that area must make a DC 22 saving throw, taking 195 (30d12) fire damage on a failed save, or half as much on a successful one. On a failed save, the target is knocked prone.

Zalthor 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. Zalthor regains spent legendary actions at the start of its turn.

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

Infernal Burst (Costs 2 Actions). Zalthor emits arcane, demonic energy. Each creature of its choice in a 30-foot radius must make a DC 22 Dexterity saving throw, taking 27 (6d8) fire and 27 (6d8) necrotic damage on a failed save, or half as much damage on a successful one.

Blinding Gaze (Costs 3 Actions). Zalthor targets one creature it can see within 60 feet of it. If the target can see it, the target must succeed on a DC 18 Constitution saving throw or be blinded until magic such as the lesser restoration spell removes the blindness or until its next short rest.

Charge (Costs 2 Actions). Zalthor charges at a creature within 60 ft. of it and makes a horn attack with advantage and doubled damage.