How to pull off a Wario Ware style "windowed" level?

[DMahannah]

Wondering what the best way to pull off the effect in the image below would be.

What I’m talking about is how the action for the level takes place in the sort of window. You can see how the shark-car is hidden past the white border of the inner frame.

My first guess was some sort of Screen Space Overlay canvas? Played around with masks in Unity, but really need more of an inverted mask option (which doesn’t exist).

What would be the best way to go about this sort of thing (when creating a 2D game in a 3D project file)?

[jwulf]

What about a PNG on an Overlay Canvas, containing (if you were to create the example from the image) the outside style and is transparent inside (PNG contains Alpha information), so you see the level there?

If the outside is supposed to be animated, using 4 rectangular Masks (as a replacement for the missing inverted mask option as you called it) would come to my mind, the “seams” could be (if necessary) hidden behind the white border, which could still be a PNG-File.