When you're a ghost you can still maledict mobs without fear of being struck. In this case, judging by context, I think Griffith may be plaguing mobs and having the plague spread naturally from that mob to PCs in the room.

I know that as a maledicting class I've often taken advantage of my ghost status to maledict mobs unmolested to ease regearing. As long as it's not a damage spell you'll be protected by the gods.