The most powerful martial artists in wuxia fiction were not merely masters of fighting technique, but also masters of manipulating their life force...their chi...to produce a number of effects from concussive power to healing. Given this, how would some of these martial artists fare against ghosts and demons, assuming that such things exist?
If you do believe in ghosts and demons, then one possible understanding of what they are is a kind of life energy that is not bound by physical laws. They exist as a kind of energy that lies beyond conventional physicality. This is partly what makes such beings so frightening and threatening to human beings: these beings can use their energy to produce harmful effects upon the physical bodies of human beings, but human beings cannot affect these beings through physical means. No sword slash or bullet can hurt a ghost, but a ghost can do all kinds of harm to a physical body (or so it is believed).
The greatest martial arts masters of wuxia fiction are not only great fighters, but also spiritually enlightened sages. Would it be possible for, say, the Janitor Monk, Central Divinity Wong Chung Yeung, or Cheung 3 Fung to use their great chi and spiritual enlightenment to battle ghosts or demonic forces?