There is a glitch on the last star on the last level. Every time i have the building claps over top of it, it can no longer grab it, it just hangs there and does not spin any more.
Beating the appretice is easy. I do it with low levels all the time. You just need someone with a range attack to do it. Just make sure there is a body of water between you and the apprentice and just let your range guys attack from a distance. The apprentice will not go around the body of water to get you.