Compared are the Theatrical Version and the Director's Cut (both available on the US Blu-ray by Scream Factory).
There are 27 differences, consisting of additional scenes in the Theatrical Version, additional scenes in the Director's Cut, alternate scenes and recuts.
15 years after the original in a small town called "Georgetown". A serial killer is on a killing spree. Some of the characteristics of the killings are similar to "The Gemini Killer" who was executed 15 years ago. The cop William Kinderman investigates the case. A clue leads him to a hospital - to the psych ward to be exact. Kinderman finds a patient there who claims to be The Gemini Killer and he is familiar with a lot of details that nobody could actually know. It turns out the soul of Damien Karras is inside of him.
William Friedkin's masterpiece "The Exorcist" was in theaters in 1973. 4 years later, the sequel "Exorcist II: The Heretic" flopped in theaters. In the early 90s, the third installment "The Exorcist III" hit theaters - directed by William Peter Blatty who produced and wrote the screenplay for the original "The Exorcist". The movis is based on Blatty's novel "Legion" released in 1983. The plot is the third installment very much diffrs from the previous ones and except for the subject possession, the movie has an entirely different story. A few known characters are in it even though most of them are being played by different actors. Even though the second sequel is not as good as the original, it is a nice and spooky thriller. Some of the scenes are quite scary actually and Brad Dourif as "The Gemini Killer" does a hell of a job.
When "The Exorcist III" was completed, director William Peter Blatty could not release the movie as originally intended. For the final cut, a few scenes were altered and cut and the ending is entirely different as well. Certainly, Blatty was not thrilled about that because the Theatrical Version was not his favorite version and he never got the chance to release his version. Almost 25 years later, Blatty made it public that he was working on his Director's Cut and he announced its release. This version is supposed to be closer to the original screenplay while the footage of the new scenes is supposed to be originated from video and film material. In October 2016, Blatty's Director's Cut was released for the very first time. Watching the Director's Cut and its new scenes, the alterations are not exactly mind-blowing. There is some additional dialog and more scenes with Brad Dourif. The remaining footage consists of redundant scenes or shots. The action-filled finale with Father Morning and Kinderman in the cell of The Gemini Killer do not even take place resp. only the Theatrical Version contains those. Moreover, the quality of most of the new scenes is pretty lousy - due to a terrible source. The Director's Cut has been released on the Blu-ray release by Scream which also contains the original Theatrical Version.
Before the actual movie begins, the Director's Cut contains some text regarding the Director's Cut.
1 min 25 sec
Director's Cut: Two shots of the stairs in front of the house of the MacNeils. The scene from "The Exorcist" follows: Father Karras jumps out of the window, winds up on the stairs and rolls down.
The movie title differs.
The Director's Cut here contains the scene from the Theatrical Version which shows the guys in the canoe on the lake.
Now, the Director's Cut contains another scene from the Theatrical Version: Father Dyer and the stairs.
Director's Cut: At the station, the prostitute also says to the cop: Dress more appropriately?
Theatrical Version: 6 sec
Director's Cut: 3 sec
Director's Cut: Kinderman walks inside. His wife Mary talks to her mom.
Mary: Do you know, Ma? When you're right, you're right! Alte Frau: Oh, is that so? Now, look, darling! Please, don't patronize me! It hurts old people when they vomit!
Kinderman puts his weapon back in the drawer and and goes to his wife in the kitchen.
The conversation between Kinderman and Pater Dyer at the restaurant is longer in the Director's Cut:
Kinderman: Nobody could do that scene like Jimmy Stewart, Father! No one! What a film, huh? So innocent, so good! It fills your heart!
Pater Dyer: Yeah, well, you said the same thing about "Eraserhead"! (Kinderman laughs).
Kinderman: Most Jews pick a priest for a friend! It's always someone like Teilhard de Chardin! What do I get? I get a priest who calls children little weirdos and treats all his friends like Rubik's Cube, always twisting them around in his hands, trying to find colors! What's the matter? You're not eating!
Pater Dyer: It's too spicy!
Kinderman: I've seen you dip Twinkies in mustard! Come on! Eat something, Gandhi! Stop fasting! The teeming masses need your strength! You're so stubborn!
Kinderman looks aside and sees a picture on the wall with several men on it. He says: I know, I know! Me too!
Pater Dyer: What a wonderful man he was, Bill! So loving, so terribly kind!
The Director's Cut shows a further picture on the wall.
Director's Cut: The nurse enters Father Dyer's room.
Nurse: I've come to take a little blood from you, Father!
Pater Dyer: Again?
Nurse: What's again?
Pater Dyer: Somebody already took it not 20 minutes ago!
Nurse: Are you kidding me?
Pater Dyer: There's a hole!
The nurse turns away from him and says with anger: There it sure is, hell, goddamn, rat shit is!
She leaves his room and yells in the hallway: Who stuck this guy?
Director's Cut: More dialog between Dyers and Kinderman:
Father Dyer: It's a drug cart! Why not?
Kinderman: Almost anyone could steal something from it!
Father Dyer: I heard about what happened at the church!
Kinderman: I beg your pardon?
Father Dyer: Father Kanavan!
Kinderman: Oh, yeah! Well, we found some kind of drug in him! He didn't feel a thing, Father! He had no pain!
Father Dyer: Ah, well, that's good!
Theatrical Version: 2 sec
Director's Cut: 22 sec
Director's Cut: Shot of The Gemini Killer (James Venamun) in his cell.
Director's Cut: Kinderman longer in front of the cell. He then looks through the window in the door. He turns away and the camera pans from the cell door to Venamun sitting on his cot.