Probably the easiest boss battle you will experience in Skyward Sword is with The Imprisoned. He looks like a sixty-foot mutant muppet and has no attacks to speak of. The only way he can damage Link is by either stepping on him, or by the shock-waves that his feet cause with each step.
To defeat this boss Link must slash away at each of his six front toes (three for each foot) and each of his two back toes (one for each foot). After destroying his toes, the Imprisoned will fall over backwards and Link will need to run around his body and lock onto the spike located on his head and perform three upward slashes. This will cause the boss to get back up and grow new toes. Simply repeat the process two more times to vanquish this unrelenting foe.