These non-playable characters are trying to imitate you, the protagonist! When you move, they imitate your movements, almost exactly! But there's a little trick in each level to finding out which one you are!

WASD or arrow-marked keys: Move yourself, or select level.
Mouse: move yellow spotlight.
Left mouse button: choose.

See if you can sleuth it out, and remember: There's only one of you! There's no one else who's just like you!