I was thinking, after Celestia settles in with most wizards, there be a new world called "Wasteland". It could be a desert, rocky, volcano world with creatures we faced in other worlds just stronger and new monsters that look ancient and powerful. The final boss in that world could be called "The Source" (short for The Source of all Evil)! He would be every school (or just death/storm). And he would look awesome! Reply to share YOUR ideas as well. :)