I made a little tool which allows you to hide stuff (in our case: whack a mole creatures) behind an object that looks the same as the background in a 2D game. Rather than having to align this object manually, this script will set the UV’s based on its entity and the background’s entity. It supports opacity maps, meaning you can get quite far with just a stretched circle.
I made a little public example scene. Hopefully this is useful to someone 
