Marnie is the first character to fall victim to the fourth Ghostface killing spree.
Marnie has the friendly face and innocence that resembles Casey Becker's.
Marnie appears at the beginning of the movie watching Stab 7 alongside Jenny. She discusses the idiocy of Stab 7's opening sequence being Stab 6, which refers to the opening of Scream 4 being that of Stab 6 and Stab 7. Jenny claims to hear a noise upstairs and goes up to investigate, leaving Marnie alone downstairs. Marnie thinks Jenny is just trying to play a prank on her.
At that moment, Ghostface calls her and asks her the infamous line, "What's your favorite scary movie?" However, it is revealed that it is only Jenny on the other end, using the Ghostface App on her cell phone to trick Marnie. Jenny hears Marnie cry out and runs downstairs to find her. She assumes that Marnie is trying to trick her and walks around the home looking for her.The real Ghostface calls her, telling her she's in his new movie now. The same movie Marnie was in but her part had gotten cut way back. When Jenny asks how, he insults her before warning her that she'd "better start running." Then Marnie's dead body is thrown through the window and Jenny runs. She is chased and finally killed in the garage.
Marnie is mentioned by Robbie after Olivia Morris dies, saying "Olivia is dead. So are Jenny Randall and Marnie Cooper." In the climax of the movie, Charlie shows Sidney Prescott a video clip of Marnie being stabbed in the stomach by Ghostface.
In the alternate opening, Marnie is the main victim. Jenny hears the noise upstairs and goes to investigate but this time when she comes back downstairs, she looks around briefly and she sees Marnie lying next to the couch seemingly dead.After a moment, she smiles and laughs. Marnie was only playing a prank on Jenny to get even, revealing she knew all along that Jenny was up to something. They sit on the couch and agreed to stop trying to scare each other saying it is bad enough they had to grow up in this town and Jenny declares Marnie the winner. Marnie gets up from the couch and goes to the kitchen to get something for them to snack on. Jenny tells Marnie "You're not fooling anyone. I think you secretly like horror movies." Marnie just vaguely says, "Maybe." What the girls didn't realize is that during their prank, the glass window was left open allowing easy access for an intruder. Ghostface was standing there for a good length of time. As soon as Marnie closes the refrigerator door, she sees Ghostface standing behind Jenny and assumes it's another prank saying, "Ok assholes, real original." Jenny just asked Marnie, "What?" as not knowing Ghostface had entered the house and is standing right behind her and then stabs her in the back.
When Ghostface starts stabbing Jenny in the stomach, Marnie thinks it a prank, but soon after sees Jenny is really screaming in pain and realizes it's for real. When she sees that Jenny is really dead, she screams as the killer turns his attention toward her with his blade and slices her arm. A short chase ensues. She rebukes him as she runs, calling him a crazy bastard at the same time. She grabs the phone off the kitchen counter and races for the front door, trying to call for help. However, Ghostface runs around to the foyer where he knows he'll meet her and grabs her from behind. Pleading, she screams, "No, please!" as he stabs her in the stomach and she falls to the ground mortally wounded.
Ghostface stands over her still alive. Marnie's last words are, "You're... not real." Then the knife dives down, making the titles come up indicating she has become another victim.
The next day, Dewey and Deputy Hicks meet while the officers are taking down the Ghostface masks from the light poles throughout the city, they are called to the Randall house for an serious situation with an officer saying, "It's Bad Sheriff, real bad." Marnie corpse's is found hung to the ceiling fan by Dewey, Deputy Hicks and other Woodsboro police where they take various camera shots of the death scene. Once the pictures are taken, Dewey immediately requests to cut Marnie's corpse down from the ceiling fan and cover them up saying, "they're just kids."
Reference to Casey Becker
Marnie's aura is much like Casey's, being innocent with the friendly eyes. Her death scene in the alternate opening is combination of Casey, Tatum and Cici Cooper's. Once she realized Jenny wasn't pranking, the killer sliced her arm (like Tatum's in the first movie). Similarities of her and Casey Becker's chases scenes are both were held and stabbed from behind by Ghostface, both grabbed their phones and held onto them the whole time, and both were gutted then hung by their neck. The only differences is that Marnie's chase was much shorter and she was stabbed initially in a vital area. Instead of being hung outside on a tree like Casey was, Marnie was hanged on the ceiling fan inside of Jenny's house.
- "You're kidding. I don't get it." (referring to Stab 6 and Stab 7)
- "I get that but it's illogical! It begs the question that if the beginning of Stab 7 is Stab 6 then is the beginning of Stab 6 Stab 5 and if so, what is Stab 4 about?" (referring to the Stab 7 opening.)
- "There's a reason I don't watch these movies."
- "I don't see how you get off on this shi- (gargles)"
- "Gotcha!" (after pranking Jenny back in the alternate opening)
- "Please! I knew you were up to something!" (revealing she knew Jenny was pranking her in the alternate opening.)
- (Sarcastically) "Nice, assholes. Real original." (in the alternate opening.)
- "Okay, Jenny. You've already had your chance to scare me." (in the alternate opening when Ghostface is killing Jenny and Marnie assumes it a prank.)
- "What are you - are you crazy?! You bastard!" (after Ghostface kills Jenny in the alternate opening.)
- "You're not real." (to Ghostface before she is stabbed and killed in the alternate opening.)
- "Jenny? I know you're gonna scare me". (when Jenny walks upstairs to investigate a noise that she heard)
- Her last name is the same as Scream 2 victim, Cici Cooper, however it is unknown if they are related in some way.
- Her casting call states: "Friend of Patty's. Funny and mischievous, loves practical jokes. Sometimes pushes too far. Bored with Woodsboro’s obsession with the murders that happened when she and her friends were toddlers."
- There is a deleted scene where the police investigate the crime scene. It shows Marnie hung from the ceiling fan and Jenny bound to a chair, much like Casey Becker and Steven Orth from Scream. This is what Gale is refering to when she asks if there's any comment on these killings paralleling the original Woodsboro murders at the press conference being held at the hospital.
- Killed by Charlie while her friend, Jenny was killed by Jill.
- Like the rest of the deleted scenes, the alternate opening was released with no score.
- She's the new version of Casey Becker from the first movie.
- Many fans have pointed out that Marnie was not a target of Jill, Jenny was. And Marnie was just at the wrong place at the wrong time. Meaning that Marnie possibly wouldn't have been killed if she wasn't with Jenny that night.
- Due to fans mixing up their names, it was once believed that Marnie's name was Trudie. It was also rumored to be "Ellie Underwood".
- Not counting Trudie, Marnie was the first person to die in "Scream 4".
- It can be assumed that Marnie died the same way she did in the alternate opening, judging from the clip Charlie shows.
- Marnie's mother attended school with Sidney. This is stated in the script by Kevin Williamson.
- In the original script, the opening went the same as the alternate opening, however, after Marnie scares Jenny, they go back to watch the movie as Ghostface approaches behind them, neither seeing him. Jenny reaches for the remote at the same time Ghostface reaches for a knife. As Jenny hits play on the remote, Ghostface strikes with the knife and it cuts to black as the opening titles appear.