Pic related is the scariest for me. The test tubes, the ominous music and how the Scientist NPCs talk about how neuseous they are from experimenting the Lake Trio makes me wonder what was going on behind the scenes. And after you battle Saturn, said NPCs just disappear.
This song freaks me out more than the lab in Veilstone Galactic HQ, though. Songs in reverse make my head hurt.
https://youtu.be/swHLZRus6WQ