I really like puzzle games, so this was cool to play. I think this is a cool mechanic with good potential to at least be explored further. Even just from seeing the beginning puzzles, there were already some clever scenarios, and I found myself thinking and having "ah-ha!" moments when I found the solutions.
I'm not sure how I feel about the skull mechanic, though. I'm not sure it adds much to the game other than complexity.
Overall cool submission!