The first puzzle in World 3 introduces the shadow mechanic. You'll see a gate that requires two switches to be pressed simultaneously. One switch is on your side, and the other is across a gap. To solve this, first, walk to the switch on your side and press it. Then, rewind time. Your shadow will now appear and press that switch. While your shadow is holding the first switch, quickly run across the gap and press the second switch yourself. The gate will open, allowing you to collect the puzzle piece. This teaches you the fundamental concept of using your shadow to hold down switches or perform actions you can't do simultaneously.
