Legend of Korra

How the heck does Lavabending work though? what's the cutoff point of the earthbending turning into firebending?

It does raise the potential for some pretty awesome stuff though, like Steambending, Mudbending ect. That's something i've always liked about Avatar, the fact there is 4 basic elements, but a lot of room for individuality and innovation between them. (like the Sandbending, Plantbending, Bloodbending and Lightningbending of the original series)

To me lavabending is just like icebending for waterbenders, lightning is just a hotter fire, plantbending and bloodbending are like metalbending as in they bend the small parts of water inside the objects and sandbending is just earthbending with a higher difficulty and I'm pretty sure we have seen steambending(in some prison and at the antibender rally) and mudbending(katara and toph mud fight).

This whole thing is why there are fans hoping we see soundbending come from airbending since sound is just the movement of air(in most cases).