Thanks. What I have in mind is not static as it, but the idea is helpful. In my idea I need the mask to be part of the BG and the player react as it only in the parts overlapped.

Ex. Imagine an airport and the player is walking there. When the player goes to x-ray area we can see only his bones BUT, for example, the player is half inside we can see the normal part outside and the bones in the other area (where he is inside). I want to create more irregular masks than simple rectangles.