Since Billy and Stu set up the narrative of the mastermind Ghostface (Billy) and the henchman Ghostface (Stu), most of the "Scream" films have followed this formula. "Scream 3" was the only film to feature a solo killer and focused on Sidney's mysterious, unknown sibling. This didn't go over well considering it's one of the worst-received films in the franchise. "Scream VI" upped the ante by having three Ghostface killers.
The reason "Scream" has stuck to this formula is because Billy and Stu proved that it works. Billy was angry that his mother left after finding out that his father was having an affair with Sidney's mother. His anger quickly turned violent as he pulled Stu into a scheme to kill Maureen Prescott and they left Cotton Weary, another man Maureen was sleeping with, to take the fall.
What made Billy and Stu such an iconic duo was their chemistry. Billy was an uncomfortable presence on screen. Always lurking about and jump-scaring Sidney (and the audience), he felt like a threatening person. Stu, on the other hand, was over-the-top, fun, and easygoing. Billy made himself look guilty constantly throughout the movie, which made him seem like too obvious a choice for the killer. On the other hand, Stu seemed way too chill to be capable of killing. Despite how different they were, though, they agreed on one thing: Learning from horror films and playing by their rules.
Two Ghostfaces makes a lot of sense for their plan to work. Having two killers means that each could give the other an alibi for separate killings and throw off suspicion on them both. In the case of the original "Scream," the reveal of the second Ghostface was also a huge twist that no one saw coming.
