User blog comment:Smijes08/Arkham Knight: Joker- Ghost or Hallucination?/@comment-16533050-20151011031731

The thing about hallucinations is that they can weave their own little threads of logic into one's mind. Seeing Barbara crippled 'firsthand' and Joker saying he 'lied' about killing Jason could just be Batman's deluded mind trying to make logic out of the situations.

Sorta like how sometimes when in a dream you can actually 'see' yourself outisde of your own body, or that you know something in a dream that dream you couldn't possibly know.