Yeenoghu, Prince of Gnolls (CR 20)

Large Outsider (Chaotic, Evil, Extraplanar, and Tanar'ri)
Alignment: Chaotic evil
Initiative: +12(+8 Dex, +4 Improved Initiative); Senses: darkvision, scent, true seeing, Listen +37, and Spot +37
Languages: Abyssal, Common, Giant, Gnoll; telepathy 300 ft.

AC: 45 (-1 size, +8 Dex, +19 natural, +9 armor and/or shield), touch 17, flat-footed 37
Hit Dice: 24d8+264 (372 hp); DR: 20/cold iron and good
Fort +25, Ref +22, Will +24
Speed: 40 ft.
Space: 10 ft.; Reach 10 ft.
Base Attack +24; Grapple +38
Attack: Melee*: triple flail +31/+26/+21/+16 *Attacks include the Power Attack feat
Damage: triple flail 3d6+25
Special Attacks/Actions: summon ghouls, summon gnolls, summon tanarri
Attack Options: Cleave, Great Cleave, Improved Sunder, Power Attack
Abilities: Str 30, Dex 26, Con 32, Int 24, Wis 30, Cha 23
Special Abilities: Spell-Like Abilities (CL 20th): At will - astral projection, bulls strength, desecrate, detect good, detect law, fly, ghoul touch (DC 18), greater dispel magic, greater teleport, telkinesis (DC 21), unhallow, unholy blight (DC 23)
Special Qualities: scent, tanarri traits; Immunities: electricity, poison; Resist: acid 10, cold 10, fire 10; SR 31
Feats: Cleave, Dark Speech, Dodge, Exotic Weapon Proficiency (triple flail), Great Cleave, Improved Initiative, Improved Sunder, Power Attack, Track,
Skills: Climb +34, Concentration +38, Diplomacy +8, Handle Animal +33, Hide +28, Intimidate +33, Jump +38, Knowledge (nature) +34, Listen +37, Move Silently +32, Ride +39, Search +34, Sense Motive +37, Spot +37, Survival +37 (+39 in aboveground natural environments or when following tracks), and Tumble +36
Advancement: -
Climate/Terrain: 422nd Layer of the Abyss
Organization: Solitary
Treasure/Possessions: +5 scale mail, triple flail, quadruple standard

Source: Book of Vile Darkness
Fiendish Codex I

Triple Flail: Yeenoghu wields a unique triple-headed +3 adamantine heavy flail. Each time he scores a hit with this item, roll 1d3 to see how many of the heads hit the target. A hit with the flail deals the same amount of damage no matter how many heads strike. If more than one head hits the same target, the victim must succeed on a DC 32 Will save or be confused for 2d4 rounds. If all three hit, the target must also make a successful DC 32 Fortitude save or be paralyzed for ld4 rounds. Only Yeenoghu can use the weapon to confuse and paralyze targets. The save DCs are Strength-based.

Summon Ghouls (Sp): Once per day, Yeenoghu can automatically summon 1d6+6 enhanced ghouls. These ghouls have maximum hit points and a +5 profane bonus on turn resistance, Armor Class, and attack and damage rolls. This ability is the equivalent of a 7th-level spell (CL 20th).

Summon Gnolls (Sp): Once per day, Yeenoghu can automatically summon 11d6 gnolls or 2d6 5th-level gnoll fighters. This ability is the equivalent of a 9th-level spell (CL 20th).

Summon Tanar'ri (Sp): Once per day, Yeenoghu can automatically summon 1d2+1 vrocks or 1d4 bulezaus. This ability is the equivalent of a 9th-level spell (CL 20th).

Updated to Fiendish Codex I

Chaotic Subtype

A subtype usually applied only to outsiders native to the chaotic-aligned Outer Planes. Most creatures that have this subtype also have chaotic alignments; however, if their alignments change they still retain the subtype. Any effect that depends on alignment affects a creature with this subtype as if the creature has a chaotic alignment, no matter what its alignment actually is. The creature also suffers effects according to its actual alignment. A creature with the chaotic subtype overcomes damage reduction as if its natural weapons and any weapons it wields were chaotic-aligned (see Damage Reduction).

Evil Subtype

A subtype usually applied only to outsiders native to the evil-aligned Outer Planes. Evil outsiders are also called fiends. Most creatures that have this subtype also have evil alignments; however, if their alignments change, they still retain the subtype. Any effect that depends on alignment affects a creature with this subtype as if the creature has an evil alignment, no matter what its alignment actually is. The creature also suffers effects according to its actual alignment. A creature with the evil subtype overcomes damage reduction as if its natural weapons and any weapons it wields were evil-aligned (see Damage Reduction).

Extraplanar Subtype

A subtype applied to any creature when it is on a plane other than its native plane. A creature that travels the planes can gain or lose this subtype as it goes from plane to plane. This book assumes that encounters with creatures take place on the Material Plane, and every creature whose native plane is not the Material Plane has the extraplanar subtype (but would not have when on its home plane). An extraplanar creatures usually has a home plane mentioned in its description. These home planes are taken from the Great Wheel cosmology of the D&D game (see Chapter 5 of the Dungeon Master's Guide). If your campaign uses a different cosmology, you will need to assign different home planes to extraplanar creatures.

Creatures not labeled as extraplanar are natives of the Material Plane, and they gain the extraplanar subtype if they leave the Material Plane. No creature has the extraplanar subtype when it is on a transitive plane; the transitive planes in the D&D cosmology are the Astral Plane, the Ethereal Plane, and the Plane of Shadow.

Tanarri Subtype

Most demons encountered outside of the Abyss are tanar'ri. The most populous of the demon subtypes, the tanar'ri form the largest and most diverse group of demons. They are the unchallenged masters of the Abyss at this time. The first tanar'ri were forged from the souls of the first humanoids drawn to the Abyss. Most tanar'ri incorporate humanoid features into their forms as a result of their close ties to the mortal realm.

Traits: A tanar'ri possesses the following traits (unless otherwise noted in a creature's entry).