I completely agree with Billy. I often find myself going back to treasures i've already gotten. It's an excellent game. Make some more like this. I'm sure this'll get badges.
If you want to see the final upgrade, just get him down to the skull and stay on the opposite end of the map and group the gravestones together, when your magic is filled and flashing, charge it all the way, and hit them, then keep the combo going and you'll be getting hundreds of experience in about 10 seconds.