Originally Posted by Aeromyre
Yes I was thinking Badger-Moles for earthbenders, but would that live up to a dragon or a sky bison? Perhaps I could make a giant badger mole
Badger-Moles are already rather sizeable. In D&D terms, they would be at least Huge sized judging by their few on-screen appearances. I would peg Dragons and Sky Bison at about the same size category.
As far as power/usefulness goes, I think they stack up rather nicely.
While flight is a definite advantage while traveling great distances due to the ability to completely bypass water (especially when traveling to the Northern or Southern Poles, which a Badger-Mole would most likely be incapable of doing), the ability to burrow as a form of transportation is not to be underestimated.
Burrowing has the advantage of stealth. As pointed out often during the show, a giant six-legged bison flying through the air is quite the spectacle. Passing underground leaves no trace at all for others above-ground to notice. This would have made things such as infiltrating Omashu and evading Zuko and Azula trivial in many cases.
Also not to be overlooked is the fact that flying and burrowing both take a substantial amount of energy to perform. However, once a flying creature becomes fatigued, it must land and become vulnerable. A tunnel already dug continues to be a safe haven, which would have made many ambushes, such as by the Rough Rhinos, a non-issue.