One of the most intriguing aspects of The Exorcist franchise was how the MacNeil family kept being haunted by Pazuzu. Linda Blair's Regan fought the entity for two films, with her mother, Chris (Ellen Burstyn), now reprising her role in the requel, The Exorcist: Believer. This time, with the original film being the only one in canon, Chris has to help save the souls of two girls who've been taken by Satan's soldier.
Source：https://www.cbr.com/exorcist-believer-ending-explained/
