Hey, so i figured out how to use the mask effect.
Make two layers and put a graphic on the bottom one which you want to show through. Then on the top one, put whatever you want to use as the mask. Then click the top layer, add the mask effect and voila!
Thing is, it seems to not refresh. If i move anything on the top layer, it leaves a trail. Anyone care to take a crack at this?
EDIT: Here's a look at a game i'm making with my first attempt at using the mask effect. The bottom layer is just a gradient and the top layer has all the sprites. See how it makes trails? How do you stop this?
EDIT 2: Oh, i just achieved the same effect by putting the gradient on the top layer and using the Additive effect.