Daphne and Niles appeared in Caroline in the City?!
Only for a few minutes at the end of an episode. In the episode, Caroline was very sick, so her friends had to write her comic strip that day for her. After much wrangling, they finally finish the strip and send it off to the syndicate, only to realize that it doesn't make any sense and isn't funny. We then cut to Niles having coffee in Frasier's apartment. Daphne is reading the funnies and asks Niles to read the confusing "Caroline" comic strip. Niles reads it, chuckles momentarily, and then says, "I don't get it."