Quoted By:
Water/Fire (or Fire/Water)
This has been something I've been waiting since Gold/Silver. And there's a TON of things that it could be, such as:
* an underwater flare or torch
* pyrophoric elements which combust when in contact with water (or water vapor), such as Potassium, Lithium and Rubidium
* steam
* hydrothermal vents and/or the life that lives with them (pictured)
Hell, it could just be some kind of abstract Pokemon with a water "shell" and a burning hot magma core or something. At least it's SOMETHING!