This art is the original rendering for the Kalibak Boulder Bomber's decals. The art is large and done in a 2:1 scale. The art possesses two acetate overlays with black line detail on each. The combination of these overlays and the painted art give the finished version.
Above you can see an image of the artwork with the first overlay removed. You'll notice (it might be hard to see from the pic) that removing an overlay removes some of the black outline detail.
Lastly we have a detailed view of the art with both overlays removed. I find this to be a very unique piece of Super Powers artwork and it is the only SP decal artwork I am aware of. This art originated from the large find of SP art showcased in Tomart's Action Figure Digest Issues 87 and 88.