Very nice prototype, I love the shadow mechanic, this also l"leaves a mark". I have a German keyboard, so z and y are switched, which always gives me some troubles on games that use z,x,c keys. The game has some bugs, the "C" was
missing in a text and it froze in the level with the two shadow blocks when I entered the door after unlocking it. If you can add a story to the game why the character got that abilities (like in Portal), this can be made into an awesome game!