I don't think Ilsidahur has ever been given official stats in any edition of D&D, though I could be wrong. He is first mentioned in Dungeon #10, in the adventure "Lost Shrine of Ilsidahur". He's mentioned in Fiendish Codex I: Hordes of the Abyss in 2006 and is briefly mentioned again in Dragon #357 in 2007.
Huge fiend (demon), chaotic evil
Armor Class 19 (natural armor)
Hit Points 362 (25d12+200)
Speed 40 ft., climb 30 ft.
Str Dex Con Int Wis Cha
30 (+10) 15 (+2) 26 (+8) 18 (+4) 21 (+5) 16 (+3)
Saving Throws Dex +9, Con +15, Wis +12
Skills Intimidation +10, Perception +12
Damage Resistances cold, fire, lightning
Damage Immunities poison; bludgeoning, piercing, and slashing that is nonmagical
Condition Immunities charmed, exhaustion, frightened, poisoned
Senses truesight 120 ft., passive Perception 22
Languages all, telepathy 120 ft.
Challenge 23 (50,000 XP)
Innate Spellcasting. Ilsidahur’s spellcasting ability is Charisma (spell save DC 18). He can innately cast the following spells, requiring no material components:
At will: detect magic
3/day each: dispel magic, dominate beast, entangle, invisibility, phantasmal force
Legendary Resistance (3/Day). If Ilsidahur fails a saving throw, he can choose to succeed instead.
Magic Resistance. Ilsidahur has advantage on saving throws against spells and other magical effects.
Magic Weapons. Ilsidahur’s weapon attacks are magical.
Reckless. At the start of his turn, Ilsidahur can gain advantage on all melee weapon attacks he makes that turn, but attack rolls against him have advantage until the start of his next turn.
Running Leap. Ilsidhur’s long jump is up to 60 feet and his high jump is up to 30 feet when he has a running start.
Multiattack. Ilsidahur makes three attacks: one with his bite and two with his fists.
Bite. Melee Weapon Attack: +17 to hit, reach 10 ft., one target. Hit: 24 (4d6+10) piercing damage.
Fist. Melee Weapon Attack: +17 to hit, reach 10 ft., one target. Hit: 21 (2d10+10) bludgeoning damage.
Howl. Ilsidahur releases a supernaturally frightening howl. The howl has no effect on barlguras. All other creatures within 120 feet of him that can hear him must make a DC 18 Wisdom saving throw or be 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. These later saves have disadvantage if Ilsidahur is within line of sight of the creature.
If the creature’s saving throw is successful or the effect ends for it, the creature is immune to Ilsidahur’s Howl for the next 24 hours.
Ilsidahur can take 2 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. Ilsidahur regains spent legendary actions at the start of his turn.
Charge. Ilsidahur moves up to his speed.
Tail. Melee Weapon Attack: +17 to hit, reach 15 ft., one target. Hit: 21 (2d10+10) bludgeoning damage. If the target is a Large or smaller creature, it is also grappled (escape DC 20). The grappled target it also restrained. Ilsidahur can grapple only one creature with his tail at a time.
The Howling King appears as a gigantic, hulking orangutan, with a long prehensile tail and bronze ram-like horns. He claims rulership of the barlguras, and is the embodiment of the brutal savagery of the Abyss. He is also served by nalfeshnee.
Ilsidahur serves the great Demogorgon, though he will sometimes quarrel with the Prince of Demons. Such is his nature, to be wild and savage. He has little interest in the politics of the Abyss, intent on hunting prey to chase down and devour. He will gladly face virtually any challenger, reveling in the violence of the moment.
The Howling King wears no armor and wields no weapon. He only uses his teeth and mighty fists in battle. He cares little for treasure for the most part, but prizes objects made of bronze.
Ilsidahur rules the 90th layer of the Abyss, known as the Guttering Grove. It is a jungle realm populated with simian monsters. It is here that the Howling King and his minions, in addition to indulging in their urges to hunt, guard the landward access to Demogorgon’s realm, Gaping Maw.
On initiative count 20 (losing initiative ties), Ilsidahur can take a lair action to cause one of the following effects: he can’t use the same effect two rounds in a row.
· Each barlgura that Ilsidahur can see can use its reaction to move up to its speed.
· Ilsidahur casts the grasping vine spell twice, targeting different areas with the spell. A targeted creature must succeed on a DC 18 Dexterity saving throw or be pulled 20 feet directly toward the vine. Ilsidahur doesn’t need to concentrate on the spells, which end on initiative count 20 of the next round.
· A tremor shakes the ground in a 60-foot radius around Ilsidahur. Each creature other than the Howling King must make succeed on a DC 15 Dexterity saving throw or be knocked prone.
The region containing Ilsidahur’s lair is warped by his magic, creating one or more of the following effects:
· Within 6 miles of Ilsidahur’s lair, creatures begin to feel as though they are being watched by something unseen. The feeling of being stalked by a predator is inescapable.
· Within 1 mile of Ilsidahur’s lair, predatory beasts become savage and nearly impossible to control. Prey animals become frightened and wild eyed, and may lash out or panic even when no visible threat is nearby.
· If a humanoid spends at least 1 hour within 1 mile of Ilsidahur’s lair, that creature must succeed on a DC 18 Wisdom saving throw or descend into a madness determined by the Madness of Ilsidahur table. A creature that succeeds on this saving throw can’t be affected by this regional effect again for 24 hours.
If Ilsidahur dies, these effects fade over the course of 1d10 days.
Madness of Ilsidahur
If a creature goes mad in Ilsidahur’s lair or within line of sight of the demon lord, roll on the Madness of Ilsidahur table to determine the nature of the madness, which is a character flaw that lasts until cured.
Madness of Ilsidahur
01-20 “I am overwhelmed with uncontrollable rage when I feel I am being challenged.”
21-40 “Violence is the solution to all of my problems.”
41-60 “I must feed on the raw flesh of my prey, devouring it like a wild animal.”
61-80 “If I want it, I take it. It doesn’t matter what it is or who it belongs to.”
81-100 “I keep and display trophies from the bodies of those I have slain.”