Mini-Ninjas Help, First Boss Fight, Lumbering Fool

I know he's called lumbering fool, but he doesn't seem very foolish, he's immune to attack!! evrytime I hti him, nothing happens! Is there some weird trick to this? Please help :(

If you are talking about the first boss go on the stairs and throw a couple of shuriken at his head until a purple thing come out and then hit it.