How do I Apply a visual mask / effect to only one layer

HI

I have a background layer.

I have a wall layer of which the player must avoid.

At the moment i have drawn my varying shapes and sizes of wall using the inbuilt sprite paint tools, all made up of varying shapes and sizes of squares and triangles. At the moment it works well, however the wall is now just one collective big black shape on the game. What i want to do is add a visual affect like a grid ontop of this, but only this ( the wall) . Is this possible to do, within the visual effect been seen on other layers?

I am playing around with the idea of making a mask layer, and then using some sort of blend mode??

So at the moment i have

Mask Layer ( grid pattern)

Wall layer ( want to see the grid on)

Background ( dont want any effect seen here)

Thanks for any suggestions.

Pete

Go File > New > Example: Blend modes. Looks like "source atop" is what you're looking for

Thanks I am playing around with these layers