Not a bad time waster.
It was really easy to win, just use all of your really expensive attacks repeatedly until you run out of mana, then keep attacking. Use all of your health refills when your health gets low, and keep attacking until your limit fills up. Use that attack, and you win.
It would have been better if there was some sort of time limit on the "press b repeatedly" function of your limit attack. Then there would be some sort of skill involved.