[quote=@Bishop]
How does the Dark Knight react to ghosts? Can he kill or absorp them?
[/quote]

The Black Knight is the lord of Death's avatar. It is likely that anything dead or undead is ultimately susceptible to both Charon's, and the Knight's will. How the Knight handles the individual ghost depends on the circumstances. If it is aggressive to the knight, chances are it will absorb or banish the ghost.