I know Pokemon is a game for kids, as much as it is for the long term fans, but hear me out when I say this: Hawaii allegedly has an orgasm inducing mushroom. Now, I know this is a stretch, but I think that this could work as a means of getting us our first Bug/Fairy Pokémon.
According to a running story, John Halliday and Noah Soule found a fungus that allegedly induced a powerful female orgasm in an instant. While it has since been proven untrue, the concept might be enough to inspire a Pokémon that induces "good dreams". Considering the more adult-themed Pokédex entries that Generation I gave us in Red and Blue, I wouldn't be at all surprised if this worked.
Maybe the Bug/Fairy adaptation could be rationalized by Parasect's need to feel wanted by the human and/or Pokémon populace? If Raichu can become a Psychic type because of sweet and fluffy pancakes, I don't see why Parasect can't do the same!