Press space or tap the screen to switch the square's direction. If you want to create your own line you have to press the green flag after setting "create line" to 1, but remember to set it back to 0 before clicking the flag or it'll reset all your progress. To add music, go to the player sprite and change the sound. Credit to Undertale for the music I used If you turn your head sideways it's a wavegame :)
