Stand on top of one of the two platforms, and then hit him with jumping slashes when he is clinging from the ceiling. The bat guy himself isn't much of a problem provided you stay out of his pattern. If he clings on the ceiling and remains still, go for it. To get rid of the bats, try to hit as many as possible with jumping slashes, being careful not to land on some bat coming from below. You can also try shooting at them from a distance. If the screen gets full of bats, use the magic to wipe them all out.