I encountered a bug, it wouldn't accept my answer even though I'm sure it is correct (photo above). My theory is that it must have created another number box and hidden it. You should add a refresh button, maybe it would have at least cleared the bug. So I restarted and took screenshots of each level so that if it happened again I could speed run the entire thing easily. Which was lucky because of a certain level later on. I think I would have just opened the game in another browser instead of replay the entire game if I had forgotten.
The game reminds me of part of my own game, where you can build bots that follow certain game rules. To build the bot you place and stack cards from left to right, and top to bottom if in roughly the same column. Maybe that could be an idea for a level where you have to zig zag like that, just not sure how you would animate a zig zag sequence.
Really good and creative game, and also bit annoying at times (which is part of the charm). I think you could potentially make hundreds of different levels without the truly gimmicky stuff if you wanted to, and even more if you include that.
Great Job! And the animation was great!