Frost Worm (CR 12)

Huge Magical Beast (Cold)
Alignment: Usually neutral
Initiative: +4 (Improved Initiative); Senses: darkvision 60 ft., low-light vision, Listen +5, and Spot +5

AC: 18 (-2 size, +10 natural), touch 8, flat-footed 18
Hit Dice: 14d10+70 (147 hp)
Fort +14, Ref +9, Will +6
Speed: 30 ft., burrow 10 ft.
Space: 15 ft./10 ft.
Base Attack +14; Grapple +30
Attack: Bite +21 melee
Full Attack: Bite +21 melee
Damage: Bite 2d6+12 and 1d8 cold
Special Attacks/Actions: Trill, cold, breath weapon
Abilities: Str 26, Dex 10, Con 20, Int 3, Wis 11, Cha 5
Special Qualities: death throes, immunity to cold, vulnerability to fire
Feats: Alertness; Improved Initiative; Improved Natural Attack; Iron Will; Weapon Focus (bite)
Skills: Hide +3*, Listen +5, and Spot +5
Advancement: 15-21 HD (Huge), 22-42 HD (Gargantuan)
Climate/Terrain: Cold plains
Organization: Solitary
Treasure/Possessions: None

Source: Monster Manual

Trill (Su): The frost worm can emit a noise that forces its prey to stand motionless. This sonic mind affecting compulsion affects all creatures other than frost worms within a 100-foot spread. Creatures must succeed at a Will save (DC 17) or be stunned for as long as the worm trills, even if they are attacked. However, if attacked or violently shaken (a full-round action), a victim is allowed another saving throw. Once a creature has resisted or broken the effect, it cannot be affected again by that frost worm for one day. The effect's caster level is 14.

Cold (Ex): Frost worms' bodies generate intense cold, dealing 1d8 points of damage with their touch. Creatures attacking a frost worm unarmed or with natural weapons take cold damage each time their attacks hit.

Breath Weapon (Su): Cone of cold, 30 feet long, once per hour; damage 15d6, Reflex half DC 22. Opponents held motionless by the frost worm's trill get no saving throw.

Cold Subtype (Ex): Cold immunity; double damage from fire except on a successful save.

Death Throes (Ex): When killed, a frost worm turns to ice and shatters in an explosion that deals 12d6 points of cold damage and 8d6 points of piercing damage to everything within 100 feet (Reflex half DC 22).

Skills: A frost worm, due to its coloration and its affinity for burying itself in the snow, receives a +10 racial bonus to Hide checks in its native environment.

Frost worms lurk under the snow, waiting for prey to come near. They begin their attack with trilling and then attack helpless prey with their bite.

Cold Subtype

A creature with the cold subtype has immunity to cold. It has vulnerability to fire, which means it takes half again as much (+50%) damage as normal from fire, regardless of whether a saving throw is allowed, or if the save is a success or failure.