Okay, this is as far as I got before sleepiness stopped me. Still unsure what the trigger was for this but at some point the displays in the museum started giving static/ electronic distortion noises. Interacting with it made thunder sound out, and then a round or so later another display made the same noise. After interacting with both, I eventually found them at wisp. They drop random loot but more often than not they dropped one mystery perk can amongst other loot. So far in one run I encountered them 4 times in these three areas. Is this a new side egg or am I behind on this?