Hi blne, A Shadow Catcher is just what the name says - that's its only function. For the kind of compositing trick you're after, you'll need to do a double render and composite them either in Phototshop or the video editing software of your choice. Create an additional plane and hide the shadow catcher. Turn the plane to black but with reflectivity, then backdrop and background to black. Render and then place this new render under the original pig and ball with it's setting as Screen.