About "Die Zauberflöte:"   the humor, I would guess, is in the spoken dialogue between the musical parts. There is one bit that is really humorous. Remember how the Queen of the Night's Three Ladies showed up and put a lock on Papageno's mouth? Because Papageno is thus corrected early in the piece -- this is done before the Queen of the Night tells the prince to go and rescue Pamina -- it isn't long before the punishment is concluded. What happens, nevertheless, is that the Prince, getting ready to go on his rescue mission, is confronted with Papageno all locked up, and the two commence a duet: the Prince pointing out that he has no magic to counter the magic lock, and Papageno, who cannot possibly cease from expressing himself somehow:

"HM HM HM HM hm hm hm hm HM hm hm hm hm HM hm hm HM hm hm HM!!!!"