Basically there are 2 windows that you can drag and drop around the screen. Whatever appears in one window will also appear in the other. The two windows cannot go one over the other.
This is a demo for the mechanic: https://youtu.be/9U4Zoagd_40?t=83
I'm looking for a few steps in the right direction. How can something like this be implemented?
As I see from a comment below there are multiple parts to a mechanic like this, my focus for now would be 2) Making each rectangle display a superposition of the level content that's behind both