Your goal in this puzzle platformer is to work your way from point A to point B by unlocking gates, manipulating the direction of gravity, and shifting yourself through negative space. (if you're not sure what that's referring to, I'd strongly recommend going back and playing Shift 1, Shift 2, Shift 3 or else you'll get stuck rather quickly). Use the ARROW KEYS to move around, press SPACEBAR or UP ARROW to jump. Press SHIFT to, well, shift. And use CTRL to switch players. Good luck!