"Night of the Ghost Fleas" is the third story in Haunted Mansion #4. It was written and illustrated by Roman Dirge.
Yet another night in the pet cemetery, and Fifi seems to be having a flea problem. She itches and scratches, wondering why the fleas are there when she as no tangible form for them to bite. Freddie the Bat takes a look and realizes they are ghost fleas. Fifi doesn't know what to do about it, and when Freddie points out that one of them is laying eggs, Fifi panics and runs, but smacks against the hearse parked outside the mansion; this only further aggravates and confuses her, especially when Freddie imagines that she might not be able to pass through the hearse because it's a carriage for the dead, and perhaps different rules apply.
Fifi starts on a tirade about her fleas, the bruise on her head from hitting the hearse, the fact that she died wearing a tutu and is stuck with it for all eternity and so on, but gets distracted by the sight of the Hitchhiking Ghosts near the gate. She yells at them that no one's going to pick them up, and calls a cab for them with a ghost cell phone she pulls out of nowhere. When she returns, Freddie tells her the source of the fleas is a literal flea circus on top of the hearse, complete with a tiny roller coaster. Freddie suggest civil discussion with the fleas to work things out, but Fifi is already smashing the circus to pieces before he can finish.
Fifi hops back down, saying the fleas won't be a problem anymore... oblivious to the fact that a new flea circus is sitting on top of her head.