Soarwhale (CR 15)

Colossal Magical Beast
Alignment: Always neutral
Initiative: +0; Senses: darkvision 60 ft., low-light vision, Listen +3, and Spot +3

AC: 14 (-8 size, +12 natural), touch 2, flat-footed 14
Hit Dice: 32d10+291 (467 hp)
Fort +27, Ref +18, Will +12
Speed: Fly 20 ft. (good)
Space: 80 ft./15 ft.
Base Attack +32; Grapple +44
Attack: Tail slap +38 melee
Full Attack: Tail slap +38 melee
Damage: Tail slap 2d6+21
Special Attacks/Actions: Breath weapon
Abilities: Str 39, Dex 10, Con 29, Int 1, Wis 14, Cha 6
Special Qualities:
Feats: Toughness
Skills: Listen +3 and Spot +3
Advancement: 33-70 HD (Colossal)
Climate/Terrain: Temperate and warm land
Organization: Solitary, pair, or pod (5-20)
Treasure/Possessions: None

Source: Arms and Equipment Guide

Breath Weapon (Su): A soarwhale quickly empties its air bladders as a defense mechanism. This loss of buoyancy causes the soarwhale to drop 100 feet, leaving a cloud of paralyzing gas in a 10-foot radius around its previous position. Any creature caught in the gas must make a successful Fortitude save (DC 35) or be paralyzed for 2d4 rounds.

In the wild, soarwhales are content to float calmly. They apparently do not need to eat, and they have no natural enemies. Their breath weapon is quite effective at fending off most predators. Sages agree the prospect of such a creature occurring naturally is slim, but if soarwhales were ever involved with magical experimentation, it happened so long ago or in such a remote location that no one has any record of it.