“Boo” is episode five of season two of Dark Angel.
It’s Halloween and Max is looking forward to a nice, normal Halloween night. Joshua wants to go out on Halloween himself; after all, everyone else is dressed up as weird creatures, and the people he’s answered the door to just think he’s wearing a costume (and quite a good one). Max refuses him, though.
Max’s Halloween gets very strange as she goes on a scavenger hunt with Joshua, a head and two other Manticore transgenics, looking for the head’s missing body. The head is still alive, even though it’s missing a body. The body is still alive too.
Things get weird and silly, for reasons that can be guessed quite early if you’re paying attention. One of the dafter episodes, all told.