Large (Outsider (Chaotic, Evil, Extraplanar)) CR 3
HP 39, hd6d8+12 AC 17 (?1 size, +3 Dex, +5 natural), touch 12, flat-fooded 14 Fort +7, Ref +8, Will +7 Speed 60 ft. (12 squares) Initiative +7 Spot , Listen
Standard attacks BAB +6, Grapple +15
Attacks
Full attack: Bite +10 melee (2d8+5) and 1d4 quills +5 melee (1d6+2)
Special Attacks/Qualities
Quills, howl
Darkvision 60 ft.
Skills Climb +14, Hide +8, Listen +13, Move Silently +12, Search +7, Spot +13, Survival +2 (+4 following tracks)
Feats Alertness, Combat Reflexes, Improved Initiative
Str 21 Con 15 Dex 17 Int 6 Wis 14 Cha 8
Alignment Always chaotic evil, Environment A chaotic-aligned plane, Organisation Solitary, gang (2?4), or pack (6?10)

Howlers live on planes where chaos and evil hold sway. A howler is about 8 feet long and weighs about 2,000 pounds. Although they are surprisingly intelligent, howlers do not speak?they only howl. If there is a language within the howls, as some have suggested, even spells cannot decipher it. Howlers understand Abyssal.

Howlers attack in groups, for they are cowardly and cruel. They prefer to charge into combat, race out, and then charge in again. A howler?s natural weapons, as well as any weapons it wields, are treated as chaotic-aligned and evil-aligned for the purpose of overcoming damage reduction.
Quills (Ex): A howler?s neck bristles with long quills. While biting, the creature thrashes about, striking with 1d4 of them. An opponent hit by a howler?s quill attack must succeed on a DC 16 Reflex save or have the quill break off in his or her flesh. Lodged quills impose a ?1 penalty on attacks, saves, and checks per quill. The save DC is Dexterity-based.
A quill can be removed safely with a DC 20 Heal check; otherwise, removing a quill deals an extra 1d6 points of damage.
Howl (Ex): All beings other than outsiders that hear the creature?s howling for an hour or longer are subject to its effect, though it does not help the howler in combat. Anyone within hearing range of a howler for a full hour must succeed on a DC 12 Will save or take 1 point of Wisdom damage. The save DC is Charisma-based. The save must be repeated for each hour of exposure. This is a sonic mind-affecting effect.

Although intelligent, a howler requires training before it can bear a rider in combat. To be trained, a howler must have a friendly attitude toward the trainer (this can be achieved through a successful Diplomacy check). Training a friendly howler requires six weeks of work and a DC 25 Handle Animal check. Riding a howler requires an exotic saddle. A howler can fight while carrying a rider, but the rider cannot also attack unless he or she succeeds on a Ride check.
Carrying Capacity: A light load for a howler is up to 460 pounds; a medium load, 461?920 pounds; and a heavy load, 921?1,380 pounds. A howler can drag 6,900 pounds.

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System Reference Document -> List of Creatures (SRD)