Jonas Larsson Grönström, who played the "Mysterious Stranger", went through the most extensive change of all actors for his part in the film. He had his dark hair bleached and coloured (making it platinum-grey), shaved off his chest-hair and his rather prominent eyebrows, and used theatrical contact-lenses to white out his blue eyes. Also, it is implied that the Mysterious Stranger is a Demonic creature (and enjoys smoking) while the actor himself is a devout Christian (and doesn't smoke).
Joel Stenström was the original actor to play the part of "Fredrik Sten", but he had to leave the project due to 'medical issues' and was replaced by Carl Carlzon Sahlén.
The psychotic Satanist-Leader (played by Adam Södergren) is only credited as "Satanist-Leader", but he was actually called "Henrik" by one Satanist (credited as "Elin" and played by Johanna Kolmodin) in one scene in the third part of the film.