Rampager (CR 12)

Large Magical Beast
Alignment: Always chaotic evil
Initiative: +2 (Dex); Senses: darkvision 60-ft., low-light vision, scent, and Spot +19

AC: 23 (-1 size, +2 Dex, +12 natural), touch 11, flat-footed 21
Hit Dice: 14d10+70 (147 hp)
Fort +14, Ref +11, Will +6
Speed: 50 ft.
Space: 10 ft./5 ft.
Base Attack +14; Grapple +14
Attack: 2 claws +18 melee and bite +13 melee
Full Attack: 2 claws +18 melee and bite +13 melee
Damage: Claw 1d6+5 plus 1d6 acid, bite 2d6+2 plus poison
Special Attacks/Actions: Acid (Ref DC 22), armor damage, fear aura, poison
Abilities: Str 20, Dex 15, Con 21, Int 2, Wis 15, Cha 10
Special Qualities:
Feats: Awesome Blow; Cleave; Great Cleave; Improved Bull Rush,Power Attack
Skills: Spot +19
Advancement: 15-25 HD (Large); 26-35 HD (Huge)
Climate/Terrain: Temperate and warm deserts, plains, and hills
Organization: Solitary
Treasure/Possessions: None

Source: Monster Manual II

Acid (Ex): The acid that coats a rampager's claws not only deals extra damage on successful attacks, it also dissolves an opponent's armor and clothing, making those items useless in 1 round unless the wearer succeeds at a Reflex save (DC 22). Success indicates that the affected equipment can be saved by washing it within 1 minute.

Washing requires a full-round action and at least 1 pint of water.

Armor Damage (Ex): A rampager's teeth can catch and tear an opponent's armor. If the opponent has both armor and a shield, roll 1d6: A roll of 1-4 affects the armor and a roll of 5-6 affects the shield. Make a grapple check (grapple bonus +19) whenever the rampager hits with a bite attack, adding to the opponent's roll any bonus for the armor or shield because of magic. If the rampager wins, the affected armor or shield is torn away and ruined.

Fear Aura (Ex): Each creature that is the target of a rampager's attack or is within 30 feet of such a target must succeed at a Will saving throw (DC 17) or become shaken. A shaken creature that is still within 30 feet of the rampager on its next turn must make a second Will saving throw (DC 17) to avoid becoming frightened (same penalties as shaken; must flee until beyond the 30-foot radius of the effect).

Poison (Ex): A rampager's acidic saliva acts as a weak poison (Fortitude DC 22) with each successful bite attack. The initial damage is 1 point of Strength damage, and the secondary damage is 1d4 points of Strength damage.

Scent (Ex): A rampager can detect approaching enemies, sniff out hidden foes, and track by sense of smell.

Something about metal drives a rampager mad. It attacks creatures wearing metal armor before anyone or anything else. Once all such targets are dead, it turns its attention to those wielding metal weapons. After all the metal nearby is demolished, the rampager starts on the largest structures in the area, ignoring even creatures that are attacking it in favor of demolishing a building (though it does defend itself once it has lost more than half of its original hit points). Only after all nearby built-up structures have been leveled does it finally turn against unarmored heroes or townspeople.