After an encounter with his species (Magog) the Rev found himself wanting to eat humans or lay eggs in them as is customary for the evil Magog. He manages to get through that but decides he need a few years of meditation to assure that he has overcome his baser instincts. I think that Rev turned out to be a bit too repulsive to make it as a regular. If he comes back I'll bet he has morphed into a different appearance.

Trance (the original) traded places with an older version of herself when they went through a temporal rift. The new version is much better than the silly Disneyesque old Trance. This may have been planned as part of the story line but more likely they are trying to tweak the series and make it better. IMO it is working. I am not a big fan but I watch almost anything scifi and this one is improving.

I am waiting anxiously for the new season of Farscape