I dreamt I was watching an episode of RGB that my brain just made up.
It began with the Ghostbusters, Slimer, and maybe Janine (I can't remember if she was there or not) outside at night time, watching the fireflies and appreciating them.
However, one of them bit Egon... and that somehow turned him into an evil firefly man! He had insect-like eyes, wings, antennae, and a glowy bit on the end, but the rest of him still looked human. But like I said, he was evil in his firefly form.
So the rest of them had to find some way of turning him back to normal.