Mivilorn, Elite Demon War Mount (CR 16)

Huge Magical Beast (Chaotic and Extraplanar)
Alignment: Chaotic neutral
Initiative: +1 (Dex); Senses: darkvision 60 ft., low-light vision, scent, Listen +9, and Spot +17

AC: 26 (-2 size, +12 natural, +6 splint mail), touch 8, flat-footed 26
Hit Dice: 30d10+300 (465 hp)
Fort +27, Ref +17, Will +13
Speed: 40 ft. (30 ft. in banded mail barding)
Space: 15 ft./15 ft.
Base Attack +30; Grapple +50
Attack: Bite +25 melee
Full Attack: Bite +25 melee
Damage: Bite 6d6+33/19-20 plus 2d4 acid (Includes adjustments for Power Attack feat)
Special Attacks/Actions: Breath weapon, charging bite, improved grab, swallow whole
Abilities: Str 35, Dex 11, Con 30, Int 4, Wis 17, Cha 12
Special Qualities: Combative mount, SR 21
Feats: Alertness; Armor Proficiency (light); Armor Proficiency (medium); Armor Proficiency (heavy); Diehard; Endurance; Improved Bull Rush; Improved Critical (bite); Improved Natural Attack (bite); Improved Overrun; Power Attack; Run; Skill Focus (Listen); Track
Skills: Intimidate +15, Listen +9, Spot +17, and Survival +11
Advancement: 31-36 HD (Huge)
Climate/Terrain: Windswept Depths of Pandemonium
Organization: Solitary
Treasure/Possessions: None

Source: Monster Manual III

Breath Weapon (Su): The save DC for an elite demon war mount's breath weapon (DC 25) is adjusted for its increased Hit Dice and ability scores.

Charging Bite (Ex): The save DC for an elite demon war mount's charging bite (DC 25) is adjusted for its increased Hit Dice and ability scores.

Combative Mount (Ex): A rider on a trained mivilorn war mount gets a +2 circumstance bonus on Ride checks. A trained war mount gains proficiency with light, medium, and heavy armor.

Skills: A mivilorn war mount has a +1 racial bonus on Listen checks and Spot checks.

A trained mivilorn is at home in the chaos and slaughter of the battlefield. A mivilorn demon war mount only uses its charge attack and breath weapon if so commanded by its rider.

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).

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.