It seems like once you apply the physics behavior to a group of sprites they all behave as though they are sharing one physical world. I would like to be able to have some interact separately from the group, as if it were on a different layer, for example multiple depth of action (excitebike comes to mind). Anyone know of the simplest way to do this? It would be simple enough to do with if-then statements in a normal collision, but the physics engine has its built in way of doing things...