In the video above you can see how Rovio coded an editable impassable ground plane for their characters to sit upon. The ground plane can also be curved and not just a straight line. What's also great about this is that they managed to align a shadow to this curving ground plane using the puppet warp tool. As a starter, does any have an idea on how to set up a ground plane like this that can be other than a straight line?
I have some theory about creating a null along a path and it's Y height acts as a clamp variable. Its position along the path is determined by the X-coordinate of your character rig using the valueAtTime and linear expressions, however, I don't know how to visually illustrate this path like they do in the angry birds' rig. Is there a way to update a shape layer's path with the position path of the null?