 The production process was plagued with problems, and changes had to be made throughout filming. "Part One"'s setting was altered after production learned of a pre-existing set, which had been used for the western television series Bordertown. The choice of location in turn influenced the type of supernatural monster that was featured. The once-epic script of "Part Two" had to be toned down due to budgetary reasons, with weather conditions forcing the episode's climax to be filmed on a sound stage rather than on location. The scenes featuring the return of John Winchester (Jeffrey Dean Morgan) had to be filmed weeks in advance using blue screen due to the actor's limited availability.
