Hey, thanks for the feedback. I know I really should work on the audio as it could add so much.
For the gameplay, you were indeed supposed to collide with the creature when it was stunned to kill it and open the exit. I don't really know how I could have made this more clear though, so if you have any suggestion I'm all ears.
As for the bug you encountered, that is unfortunate, I'm not sure what could have caused that, but in my experience the html5 seems buggier than the other versions and after trying to recreate your bug it does not seem to malfunction on my end.
On your last point, it indeed is all lighting and a shader to hide things. As for raycasting I avoided it because I couldn't get it to ignore part of the tilemap and have instead used a line supercover algorithm to check if the player could be entirely seen or not.
I can upload the code if people are interested, but I can't guarantee its quality.