So I want a NPC to follow the party, but not along the streets. This NPC will take to the rooftops to keep an eye on the group with Climbing-20 and Acrobatics-20. They obviously don't want to be seen, so how should I play that out? I thought about Shadowing, but that says 'follow another person through a crowd' and the NPC is not in the crowd. Would it just be a simple Per roll, likely at a penalty, for the group to notice the person on the roofs tailing them? Would Stealth be involved? Would there be any contest at all, or just a Per roll from the group? is there a skill I missed? Could there be an optional specialization of Shadowing for this? Looking for ideas and opinions, please?