maxgeek, just keep jumping near his tentacle and slashing. if it looks like he will 'shake' his tentacle jump away, because he can't be hit then. if he looks like he will swing his tentacle, jump it twice as it passes under you. Keep slashing, you need to do it fast so the other tentacle doesn't grow back. Once you knock off both tentacles quickly use your 'circle of flame' ninpo and go wild on him with combos. Repeat. I only had to do this twice before he was dead.