Remorhaz (CR 7)

Huge Magical Beast
Alignment: Usually neutral
Initiative: +1 (Dex); Senses: darkvision 60 ft., low-light vision, tremorsense 60 ft., Listen +8, and Spot +8

AC: 20 (-2 size, +1 Dex, +11 natural), touch 9, flat-footed 19
Hit Dice: 7d10+35 (73 hp)
Fort +10, Ref +6, Will +3
Speed: 30 ft., burrow 20 ft.
Space: 15 ft./10 ft.
Base Attack +7; Grapple +23
Attack: Bite +13 melee
Full Attack: Bite +13 melee
Damage: Bite 2d8+12
Special Attacks/Actions: Improved grab, swallow whole
Abilities: Str 26, Dex 13, Con 21, Int 5, Wis 12, Cha 10
Special Qualities: heat
Feats: Awesome Blow; Improved Bull Rush; Power Attack
Skills: Listen +8 and Spot +8
Advancement: 8-14 HD (Huge); 15-21 HD (Gargantuan)
Climate/Terrain: Cold desert
Organization: Solitary
Treasure/Possessions: None

Source: Monster Manual

Improved Grab (Ex): To use this ability, the remorhaz must hit with its bite attack. If it gets a hold, it automatically deals bite damage and can attempt to swallow the opponent.

Swallow Whole (Ex): A remorhaz can try to swallow a grabbed opponent of Large or smaller size by making a successful grapple check. Once inside, the opponent takes 2d8+12 points of crushing damage plus 10d10 points of fire damage per round from the creature's blazing gut. A swallowed creature can cut its way out by using claws or a Small or Tiny slashing weapon to deal 25 points of damage to the remorhaz's gut (AC 20). Once the creature exits, muscular action closes the hole; another swallowed opponent must cut its own way out. The remorhaz's interior can hold two Large, four Small, eight Tiny, sixteen Diminutive, or thirty-two Fine or smaller opponents.

Heat (Ex): An enraged remorhaz generates heat so intense that anything touching its body takes 10d10 points of fire damage. This is usually enough to melt non-magical weapons, but magic weapons get a Fortitude save (DC 18).

Tremorsense (Ex): A remorhaz can automatically sense the location of anything within 60 feet that is in contact with the ground.

Skills: Remorhazes receive a +4 racial bonus to Listen checks.

Remorhazes hide under the snow and ice until they hear movement above them, then attack from below and surprise prey.