Could Shadow People Be Demons?

Shadow people could be souls from purgatory that are manifesting as part of working out whatever they need to work out before going to heaven. Just because you see an apparition as a dark, indistinct form, doesn't mean it's a demon. Black cats aren't really servants of the devil. No matter how ill tempered cats can sometimes act. The christian faith recognizes the existence of departed human spirits or ghosts. And catholic tradition recognizes that god may sometimes allow them to appear to the living.