Wavefire

A handful of scholars argue that the Inner Planes were once laid out differently, with the four elements in another order and so different border planes between them. In that lost pattern, they claim, Earth and Air formed a para-elemental Plane of Dust full of choking sandstorms rather than decay, and Fire touched Water to create a Plane of Steam: an endless, bottomless ocean at a rolling boil beneath a sky of vapor. Riding the surface of that sea were the wavefires, more or less boiling water elementals.

The wavefires certainly exist. The 'alternate planes' camp says that ages ago the Inner Planes shifted into their present order, by themselves or at some unknown hand, wiping out nearly everything from the old order except the wavefires, and they hold up the creatures as proof. They are the only proof, though, and skeptics point out that a creature fitting its home poorly may just show how little sages really know about the quasiplane of Steam. Some suspect the theorists of having their own angle in spreading the tale.

A wavefire fights simply. It races at its foes and smashes them with a surge of boiling water for 3d6, and anyone hit must also save vs. breath weapon or take another 2d6 from the scalding heat, or 1d6 on a success. Its fluid body and speed give it its excellent Armor Class; stranded out of water, say after a clever wizard teleports it away, it moves at only 3 and drops to AC 6.

Only +1 or better weapons harm it, and heat and fire have no effect. Part water and lower water do nothing to it either. Cold saps its essence, though: a cone of cold or similar attack deals double damage and halves its movement for 1d3 rounds.

The quasiplane of Steam is cool, damp and misty, yet the wavefire is boiling hot and darts through the mists with speed and fury, an angry, alien thing that seems out of place even at home. Now and then one turns up on the Elemental Plane of Water, never for long, since the cooler liquid there would eventually kill it. Travelers sometimes spot small packs hunting together, but competition for food soon breaks them up and each wavefire ends up fending for itself. The quasielementals and mephits of Steam give wavefires plenty of room without respecting them much, and the wavefires barely notice anyone.

A wavefire feeds on dry air, soaking it into its scalding body, which makes the lungs of visitors, dry by the plane's standards, an obvious meal. Otherwise it hunts for bubbles of pure air leaking into the plane. Could the planes really have been arranged differently once? In a multiverse this strange, perhaps, but resting a whole theory on one ill-fitting creature strikes most folk as storytelling rather than scholarship.