After the game started, Hit Ctrl + Shift + ~ and it will bring up the Console.
In there, Type "Developer true" (Ignore the quotes)
Here are some Commands that I know:
D - Kill all of the balls in the Screen
F - Spawn Fireball
L - Spawn Lightning Bolt
P - Show paths
C - ???
R - Retry Stage
N - Skip to next Stage
Scroll Lock - Screen Editing Mode
O - ???
F11 - Show FPS
F6 - Turn off all Effects?