i know exactly what your talking about and i remember that episode to! sadly idk the name sorry. but the guy above me's right about it being shown on dexters laboratory.
It SHOULDN'T of happened.
Th bending effects were trash. There were barely any fighting scenes anyway. The rocks moved so SLOW. And I didn't like the firebending from a source either. I actually really disliked Zhao & the Firelord. They looked like they could be twins. They looked too much...