@awk If you have ever been spelunking and gotten to the point in the expedition where the guide asks everyone to turn off their headlamps for a minute, you realize that true total darkness is pretty darn creepy.
Ball Lightning - but you might have to wait a long time for that.
St. Elmo’s fire is pretty creepy, and not as rare as Ball Lightning.
Of course if you can’t wait for nature to take the initiative, Jacob’s Ladders or Tesla coils are great choices. I have a UVC-Ozone lamp that lights up a room in the sickliest death-pallor green I’ve ever seen (through UV safety goggles), but it’s probably a poor party choice. PSA - don’t look at UVC lamps unless you really want to get UV burns, possible blindness, cataracts and skin cancer).