Exorcist II: The Heretic with the idea of directing a sequel, explaining that "every film has to struggle to find a connection with its audience. Here I saw the chance to make an extremely ambitious film without having to spend the time developing this connection. I could make assumptions and then take the audience on a very adventurous cinematic journey." Linda Blair agreed to reprise her role of Regan MacNeil for "Exorcist II", but refused to wear demon make-up (a double was used for the brief flashback scenes depicting a demonic Regan). Max von Sydow was persuaded by Boorman to reprise the role of
The Exorcist III an effects-laden exorcism sequence featuring Nicol Williamson as Father Morning, a character added just for the new climax. Blatty had to make the best of it in the narrative while racing to complete the film. Blatty confirmed that when the possessed Karras speaks in an asexual voice, saying, "I must save my son, the Gemini", that this in fact is either a returned Pazuzu or, as Blatty put it, "Old Scratch himself" taking control. This ties into the revelation earlier in the film that the Gemini was sent into Karras' body as revenge for the Regan MacNeil exorcism. The altered