How does grappling a mounted opponent work? Presume monster A is attempting to grapple PC B who is atop his mount. Does the PC get any bonuses? Does it automatically unseat him from the mount? If not, if PC orders mount to move away, does that give a bonus?
Now throw a wrinkle in this. Say the PC has the Equestrian Belt. This says he "automatically succeeds at any check to guide with the knees, stay in the saddle, fight with a combat-trained mount, control a mount in battle". Does this mean the PC cannot be removed from the saddle? Does the mount join the grapple?