Very fun game! I managed to beat it after a couple of tries!
Did find a bug that made beating bosses much easier though. At least I don't think it was intended to be a feature. If you spam light attacks with one ghost and then press the swap ghost button you can get the other ghost (usually the sword ghost) to appear and keep doing light attacks automatically while you still have the first ghost out. So you have two ghosts out at the same time.