Indeed, the shadow concept might have been seen quite a few times, but the increase and decrease elements, along with how they alter the opposite shadow, are new to me. They open up whole new possibilities, which have been complemented with other game elements quite neatly. The level design also makes exhaustive use of these possibilities. It was very entertaining.
Just one minor bug: When resetting, the timer doesn't stop. You have to go to the level selection and re-select the level to reset the timer.