Pause the game with the left mouse button and then press up up on the joystick ten time. You should hear a ping sound, letting you know it worked. Pause the game again and push the joystick in one of the following directions:
Joystick Down-------Puts you in slow motion
Joystick Right--Toggle invincibility on/off
Joystick Left------Select between power ups
The right mouse button will allow you to skip levels.