This is a great start for an interesting game. Being able to solve puzzles different ways is a cool idea and could be extremely fun. I figured out all the rune combinations without the GDD, and looked at it anyway just to be safe to confirm.
I got what I felt like was a decent way into the game. I made it over the wide fire pit and several rooms after. I lost when I swapped worlds and an enemy was spawned directly on top of me, which brings me to my one major complaint. A death like that felt a bit unfair, and detracts from the experience a bit. Doing the puzzles up to that point feels rewarding, and being sent back to the very beginning because an enemy just appears without warning was painful. A checkpoint or something would make that feel a lot less bad. Maybe seeing shadows of enemies in the "other world" or something before you teleport?
I had quite a few bugs, but most of them felt like it was a problem of the game being in the browser, more than it was the game just being buggy. Unity games tend to run weird in the browser for me, so I can't say for sure one way or the other. The fireball meter got stuck on the screen almost every time I used it, the wings just didn't work at all one time I tried to jump the fire pit. The wings appeared, but didn't lift me up. Again, these could all be browser issues that don't appear on a windows export.
Don't let the "negative" things I wrote take away anything from the game. I played it longer than I thought I would, because it really is fun. Expand on this, and keep developing things! I enjoyed my time with this, and will probably come back and finish it at some point. When I do, I'll post a reply to my comment here!
Great job!
edit - I went back and did it, way sooner than I expected to. I felt I had a good grasp and didn't want to leave it unfinished. I even found the special rune I believe. Thank you again! I still love the concept!