Thanks to paradon for the review!
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Items:
Red: Deadly.
Grey Marble: The marble you try to get to the end.
Dark Red: Draggable deadlies.
Green: Arrow keys to move these left and right.
Yellow: Draggable and not deadly.
Teal Blue: Deflecter that bounces the marble in a certain direction. Only found in Arcade machine.
Blue: Gears. Rotatable.
Purple: The end of the level, where you try to get the marble.
White: Spins when you press arrow keys.
A tip for level 4: Drag the barrier up and then over to the next.