Large fiend (devil), lawful evil

Armor Class: 19 (+1 plate armor)

Hit Points: 402 35d10+209

Speed: 20 ft , fly: 60 ft , climb: 20 ft , can hover

STR

20 +5

DEX

18 +4

CON

23 +6

INT

20 +5

WIS

14 +2

CHA

22 +6

Damage Vulnerabilities: effects that target an area

Damage Resistances: Cold, Fire, Lightning; effects that target a specific number of creatures

Damage Immunities: Poison

Condition Immunities: Charmed, Frightened, Paralyzed, Petrified, Poisoned, Prone, Restrained, Stunned

Senses: Darkvision (Devil's Sight) 120 ft.

Languages: all, telepathy 120 ft.

Challenge Rating: 22 ( 41000 (or 50000 in Lair) XP)

Proficiency Bonus: +7

Actions

Multiattack. Baalzebul uses Disease Equalizes Lesser and Greater Men (if available), then makes 4 Keen Edge attacks.

Disease Equalizes Lesser and Greater Men (Recharge 5-6). Baalzebul channels pestilence into his body, sickening creatures within 50 feet that can see him. Sickened creatures must make a DC 21 Charisma saving throw, followed by a DC 21 Constitution saving throw. Failing the Charisma save makes a creature have the frightened condition, while failing the Constitution save makes a creature weak. While weakened, a creature deals half damage on melee attacks. Both effects last for 1 minute or until cured by any effect that would remove Exhaustion.

Keen Edge. Melee Weapon Attack: +12 to hit, reach 5 ft., one target. Hit: 14 (2d6 + 7) slashing damage. When Baalzebul rolls 20 to attack a creature, that target takes an extra 14 slashing damage. The target then rolls a d20. If the result is a 1, Baalzebul lop off one of the target's limbs, with the effect of such loss determined by the DM. If the creature has no limb to sever, he lops off a portion of its body instead. In addition, he can speak the sword's command to cause the blade to shed bright light in a 10-foot radius and dim light for an additional 10 feet. Speaking the command word again or sheathing the sword puts out the light. When Baalzebul attacks an object with this magic sword and hits, he maximizes the weapon damage dice against the target.

Reactions

Usurpation. When a creature within 30 feet of Baalzebul targets itself with a spell or effect, Baalzebul can use his reaction to gain the same effects as the caster (including interacting normally with a caster using time stop). Baalzebul can have only one usurped spell effect at a time; copying a new effect causes him to forfeit any previously copied effect.

Legendary Actions

Keen Edge. Baalzebul makes a Keen Edge attack.

Implant Fear (Costs 2 Actions). Baalzebul targets a creature he can see within 60 feet of it. The target must succeed on a DC 21 Wisdom saving throw or take 44 (8d10) psychic damage and immediately use its reaction, if available, to move as far as its speed allows away from Baalzebul.

Swarm Form (Costs 2 Actions). Baalzebul and all his equipment collapse into a cloud of flies that occupies a 10-foot cube, and he moves up to his speed without provoking attacks of opportunity. While discorporated in this way, Baalzebul can pass through the spaces of other creatures with this movement. Each creature Baalzebul moves through must immediately make a saving throw against Biting Blackflies unless it has already been affected by Biting Blackflies this round. Baalzebul reforms to his humanoid shape when he ends his movement.

Lair Actions

On initiative count 20 (losing initiative ties), Baalzebul can cause one of the following effects; he can't use the same effect two rounds in a row:

Affliction of the Flesh. Baalzebul infests one nonmagical object, corpse, or section of the environment no larger than a 5-foot cube within 60 feet with a parasitic growth. This growth bursts open on initiative count 1 (losing initiative ties), spreading vile mist in a 15-foot-radius sphere of itself. Creatures within the radius must make a DC 21 Constitution saving throw or take (11) 2d10 necrotic damage and be unable to regain hit points until the end of their next turn. On a success, the creature takes half as much damage and can regain hit points as normal.

Malady of the Mind. A psychedelic pattern of twisting shapes appears in the air at a point Baalzebul can see within 120 feet of him. Each creature other than a devil that can see the pattern must succeed on a DC 21 Intelligence saving throw or have a -1d4 penalty on the next Wisdom saving throw it makes before the next initiative count 20.

Sickness of the Soul. Baalzebul attempts to erode the will of hostile creatures. Up to 3 creatures of his choice within 120 feet of him that he can see must make a DC 21 Charisma saving throw or gain 1 level of exhaustion as their spiritual resilience falters. A creature is immune to additional exhaustion imposed by Sickness of the Soul for 24 hours after succeeding on a saving throw against it or after the exhaustion imposed by this Lair Action ends.

Regional Effects

The region around Baalzebul is warped by his corrupting presence, creating one or more of the following effects within 1 mile of his lair, which fade over the course of 1d10 days if Baalzebul dies:

Plague Rats. Vermin that carry a disease experience its effects but cannot be killed by the disease.

Corruption Abounds. Creatures that aren't allies of an archdevil have disadvantage on ability checks that rely on Charisma (Persuasion) skill checks.

Hallucinations. Creatures with an Intelligence score of 7 or higher regularly see mirages and experience similar visual hallucinations.