oh.. sorry about that. I had to explain it in the description. There is a "Story" button inside the game where you can see what has happened.
Story:
There was a slime. He lost his shadow, so it went in the past.
And now you have to complete all the levels to get your shadow back.
Game:
There are 3d levels, but you see them in 2d, cause they are like reflections on the walls. So, you have to find out where is the other dimension and complete the level. When you did that (went into the portal) then your past version (your shadow) begin to repeat your actions. So, you have to complete the level in the way that the shadow will do that too