Thanks for your great feedback. The music was actually written specifically for the game by Tunglith, who I've cooperated with for all my games so far.
Yeah, there is definitely an easier and a harder room in the end, but I wanted players to choose freely between them. The room with the two ghosts actually gets easier once you get what the mutation is actually doing. It resets ghosts that are chasing after you, the idea is that you mutate into a ghost, so they would not attack you anymore. So effectively it's: night vision, speed boost, ghosts ignore and can't harm you. And you can't really 'waste' it because you can build up your ghost level again with every three new ghosts you drink. I actually want to include the ability to float through crates like the ghosts can as well, but still need to figure out how to handle what happens when you end ghost mode while standing inside an object...
I agree with you though, that it needs to be set up correctly. Initially the setup for the mutation was the second ghost that corners you when you get the key in the dark passage. But the gameplay of drinking and immediately mutating was not fun, because it was really passive and sometimes you would have to get into ghost mod and wait for it to pass, just to empty your flask to get a ghost out of your way. So I changed it to the current system, but didn't have time to change the level design to match it and also didn't get to make a text explanation for it before the deadline. I plan to address this in a future update though.
Thanks for all your notes! They were really helpful