IDE :: Inverse - Hiding The Masked Object Instead Of Revealing It

I've taken this problem far and wide, and it's a common one, too: Someone wants to use a mask inversely, hiding the masked object instead of revealing it. The only coded solution is to create a bigger "stage" mask with the inverse mask cut out. I understand the process, and have a slight grip on methods of executing it. Too bad it still will not work properly. I have employed two solutions to no avail. There was this simple option, and then there was this slightly harder option.

And where it works for some people, it is not working in my instance. If you look at my files, the masks cut out rather strangely. Is there something different about this situation that requires a different line of code, or am I simply using it wrong? To show you how they worked out, this is the goal: And this is what I ended up with after option 2: Because the object will be squishing and changing shape, creating the mask frame by frame would be a hassle. Changing the shape of a solid mask is a lot easier than moving the particular points of a "stage" mask manually.