Overall a fun experience. My biggest issue was clicking "Retry" after losing taking you back to level 1 instead of retrying the current level, but I'm sure that's a simple change. I did crash a handful of times when retrying or returning to the menu, but my progress was saved when I refreshed, so that was more of an annoyance than anything. Wonderful visuals and music, although it would have been nice for more of a difference in sound effects between cavers reaching the end and bats killing them. Difficulty curve was not too flat and not too steep in my opinion, and that tutorial was great! Caving in the mountains fits the theme imo, although sadly there was no fog, so I have to give 1 star for that. Maybe you could have had fog blocking parts of paths but show cavers', bats', walls', and maybe rocks' silhouettes through it? Regardless of any criticism, though, I had a blast playing this, and I made it all the way to the end!
If you want to continue with this game, one more suggestion I have is an adjustment to the mouse movement. If I have my cursor up against a wall on my right, and I move my mouse diagonally up and right, then when I come around a corner that allows me to move right, the cursor suddenly teleports further right, seemingly to where it would have been if the wall hadn't been there at all, so it seems like there's some desync between the actual mouse position and what shows up on screen.