I rushed this code out this morning, so don't expect it to look pretty. However, for the teachers, if you don't have anything to do during the latter half of class, you can use the Multi-player version of the game.
basically the stuff that makes snap blocks and sprites and buttons appear and look the way they are is called morphic.js, made for snap by the primary snap developer, jens, and the OP is using morphic here to create other stuff. it is allowed :)
correction: his name is jens
also, I would recommend switching this to Share your Projects because advanced topics was created for normal/newer users to kinda stay away from really advanced stuff, and while this is morphic which counts as advanced, I would think newer users should still definitely see this project.