Hello there, I just finished your demo, it was really fun!
I like the art style and the sound design a lot, and the whole game idea is very nice, I enjoy that type of puzzles.
You did a really good job, so I have only a few bits of feedback for you.
1. Healing water placement is a little bit punishing in the middle game, the second one feels like a secret. I feel like adding at least one more of them and placing them in less hidden spots would be fine. It is important because some rooms require the player to return to the respawn point to heal. However, the teleport system did a great job in the final part of the game.
2. Some things (very few) could be better explained, like differences between weapons. A window with a short description that pops up when the weapon of given type is picked up for the first time should be enough.
3. It could be a good idea to make boss copies a little bit more distinguishable (maybe some phasing effect?). Sometimes the boss is pretty far away and if we spend too much time searching for the right one we may not be able to reach him.
4. I think that I found red clothes at one point, but they didn't show up in the menu, so I couldn't wear them.
These are the only things that I can think of now - all the rest is fantastic. I would definitely play it more sometime.