I LOVED THIS. One of my favourite entries of this jam: give me some clever mechanic to change the world's rules, and I will fall madly in love with it. *-*
It's a pity that you managed to create only four levels (I surely know how time runs away faster during the jams :P), but I enjoyed all of them a lot. The core concept is so powerful and well implemented that there's a lot of potential for a complete game, here. If you'll ever add more, I'll be glad to play again and again. The reminders to the masterpiece Baba is You (which I also love) are clear, as you stated in the comments; well, that's not something easy to be compared with, but I believe you did a great, great job :)
If I may add some critique (just wanting to be constructive - my overall opinion is hugely positive), there's one important thing that you have to consider when you give so much freedom and power to the player: borderline cases and exceptions. The player will try to (...well, I tried to) break the game by pushing the rules to the limits, and the game should allow the player to experience the consequences. For instance, I saw that you allowed the spawning of multiple main characters (that's the kind of borderline cases I was referring to). I was amazed when it happened, because it was possible by the rules and it was also possible in the game: that really felt like I was able to do everything, and the game seemed fair. However, this lasted two seconds, then the game broke and I was forced to restart. That felt unfair, because it was like the game was lying about my possibility to put anything in the rules' slots, and in the reality there was only one scripted solution.
Of course, I know that managing exceptions is not the easiest thing, especially during a game jam, and just the fact that I could see four main characters on the screen was wonderful. My comment is just to tell you something about my experience, from the perspective of someone who deeply loves this type of games to someone who -I believe- does too. I do not mean to tell you what to do, or that the game is incorrect; I'm just wondering about things :)
In conclusion, thanks a lot for the submission, I loved it and I hope that it doesn't stop here. Congrats!