Here are some methods of Beating Sensei that work! Dont believe me? Check out this vid:
Methods For Beating Sensei
Method 1: Select Water, Water, Water
Method 2: Select Fire, Water, Water
Method 3: Snow, Water, Water
Method 4: Fire, Fire, Water
Method 5: Snow, Snow, Water
Please note that you must be a black belt in order to beat Sensei!