thanks for the suggestions guys
but neither is exactly what I meant
let's say you have a background
and you want to see the whole background at all times
on top of the background (on the next layer) you have a sprite of a ghost and a circle
you don't want to see the circle, but you want to use the circle as a mask to reveal the ghost
so the ghost is invisible except for parts that are overlapped by the circle
I can do this by making a huge transparent square sprite with an opaque circle in the middle and using mask, or a huge opaque square sprite with a transparent circle in the middle using erase. I'm trying to figure out a combination of layer and sprite effects, where I can just have the circle by itself, without needing a huge square around it. even if I need a huge square sprite I have to reuse, I don't mind. I just want the circle I'm using as a mask to be separate from the huge square, so I can move it and reshape it freely without worrying about whether the square is covering the rest of the screen.