Can you knock an opponent prone that is grappled, or grapple a prone target, and the effects stack?
Makes sense it would. Was actually just scanning the boards about just that question. Usually you think of someone pinned, it could be like a full nelson standing up, but usually wrestling goes to the ground, with the one on the botton at a significant disadvantage to the one of the top.
I was considering ruling that the controlling grappler can move the defender prone per the Move option when sustaining a grapple, but has to then Kneel themselves. So the defender would get -4 to their CMD and CMB, but the controlling grappler would also get a -2 to their CMD (netting the defender a -2 on trying to break the hold after being put on the floor, while giving the conrolling grappler an effective addintional +4 to maintain a grapple/pin). So a common grapple strategy would be to gab, throw to the ground (to max the chance they own't be able to break the pin), then try to pin. That follows real wrestling, and common sense.