Nightmare Beast (CR 15)

Huge Magical Beast
Alignment: Always chaotic evil
Initiative: +1 (Dex); Senses: darkvision 60 ft., low-light vision, and Spot +13

AC: 21 (-2 size, +1 Dex, +12 natural), touch 9, flat-footed 21
Hit Dice: 15d10+105 (187 hp); DR: 15/magic
Fort +16, Ref +10, Will +6
Speed: 30 ft.
Space: 15 ft./10 ft.
Base Attack +15; Grapple +19
Attack: 2 tusks +22 melee and 2 claws +20 melee and bite +20 melee
Full Attack: 2 tusks +22 melee and 2 claws +20 melee and bite +20 melee
Damage: Tusk 4d6+9/17-20, claw 2d4+4/19-20, bite 4d6+4/19-20
Special Attacks/Actions: Nightmares, spell-like abilities, trample 4d6+13
Abilities: Str 28, Dex 13, Con 24, Int 8, Wis 13, Cha 11
Special Qualities: Augmented critical, SR 20
Feats: Cleave; Improved Critical (tusk); Improved Bull Rush; Improved Overrun; Multiattack; Power Attack
Skills: Jump +24 and Spot +13
Advancement: 16-30 HD (Huge); 31-45 HD (Gargantuan)
Climate/Terrain: Any land
Organization: Solitary
Treasure/Possessions: 1/10th coins; 50% goods; 50% items

Source: Monster Manual II

Nightmares (Su): Perhaps the nightmare beast's most powerful weapon is the one from which its name is derived. Every intelligent creature that falls asleep within 10 miles of a nightmare beast must succeed at a Will save (DC 17) or suffer from horrid, vivid nightmares of being stalked and killed by monsters, demons, cruel enemies, or whatever else it fears. The effect is otherwise the same as that of a nightmare spell (caster level 15th; Will save DC 17), except that a dispel evil spell cast on a victim does not stun the nightmare beast. A remove curse or a successful dispel magic negates the effect. Once a creature has either been affected by this ability or made a successful save, it cannot be affected by that nightmare beast's nightmare power again for 24 hours.

Spell-Like Abilities: 2/day - chain lightning, cloudkill, dimension door (1,000 ft. range), disintegrate, dispel magic, fireball, heat metal, incendiary cloud, lightning bolt, monster summoning V, wall of fire. Caster level 10th; save DC 10 + spell level.

Trample (Ex): As a standard action during its turn each round, a nightmare beast can trample opponents at least one size category smaller than itself by making a running jump from up to 35 feet away This attack deals 4d6+13 points of bludgeoning damage. A trampled opponent can attempt either an attack of opportunity at a -4 penalty or a Reflex save (DC 26) for half damage.

Augmented Critical (Ex): A nightmare beast threatens a critical hit on a natural attack roll of 19-20 with any of its natural weapons.

Few monsters aside from dragons are as dangerous as a nightmare beast. The creature attacks anything that looks like food with its teeth, tusks, and claws, dealing massive amounts of damage by means of its augmented critical ability. And in spite of all that damage potential, its most dangerous weapons are its spell-like abilities.