I'm on level 10 so far, having fun :)
-The buttons and menus already work on mobile, having the option of touch screen swipes as well as arrow keys would be great.
-An undo/redo would be great, I just watched your lesson on it, so I know you know how!
-Restart/undo hints when the puzzle is unsolvable due to misplating would also be stellar!
Thanks for sharing!