This game is very well done. I love the concept and atmosphere it has.
I wanted to detail a few things I discovered, but it also does involve spoilers, so don't read this if you haven't played the game!
First, the note.
When you click on it, it says "This place isn't what it l-" and then says you can't read the rest, however if you look closely at it without clicking on it you can see it reads "This place isn't what it seems, go back!" Maybe it's a stock texture, or maybe originally it wasn't going to be unintelligible; either way, I think that's neat.
Second, the monster.
If you look into the files of the game, you will find that the model of the monster is actually split up into several pieces for it's legs and what not. However, if you look at the head part of the monster, you will find that it's name is "uploads_files_1961068_beholder_whole," which leads me to believe that the name of the monster is simply "Beholder." I thought that was neat too.
Last, the music.
There is, very surprisingly, a lot of interesting stuff about the music, especially when you look at it compared to the official release. One file is exactly the same as it is on the soundtrack aside from audio quality, that being Title Screen / Credits; the only thing of note is that it has the label "(MASTER)" at the end of it's name. Past that track is where things get interesting. Most of the other tracks didn't really have names, the track Escape Plan simply goes by "Gameplay - Main" and doesn't have a fade out effect, and the track Phase Two doesn't have a fade-in effect and goes by "Gameplay - Stage 3." Now you may be thinking, "Stage 3? Aren't there only 2 stages?," and you would be right. However, there is some unused music in the game that makes this name make sense, sort of. There are 2 tracks that go by "Gameplay - Stage 1/2," which are very clearly related to Stage 3 in that Stage 1 is just the percussion from Stage 3 and Stage 2 is just the bass from Stage 3. I have a theory that this means the music was meant to get more intense as you burned through your 5 minutes, but we may never know. The last interesting thing is the music for the ending, which is actually split into 2 parts. Part 1 is titled "Seren Exit (MASTER)" (which is part of the name on the official release), while part 2 is named "Monster Reveal (MASTER)." There isn't a ton different about it except, if you stitch them both together, it's a couple seconds longer than the official release since there are a few seconds of silence at the end of Seren Exit.
Mr. Klubnika, I am very, very sorry if you don't appreciate people looking through the files of your game. I truly do love this game you've created and only did it out of curiosity, not out of malice, so I hope you can understand. Maybe you could even shed some light on these things!
Also... thanks for reading all this, I realize now it's quite a bit.