Greater Conflagration

This skill is... well... no where? lol... if you find it, or know a general area it is found at, respond. I've already been told it's in the desert area, but i havent seen any bosses use it. It's a spirit too, so i dont know how "easy" it's going to be...? but i think since it's a spirit ritual it should be easier to find (guess i was wrong).