Minor Plot hole: In the Prelude of the second murder, Ghostface convinces Jill and Kirby to open their closet, making them fear that he is inside of it. He then screams in the phone that he didn't say he was in THIS closet. He then jumps out of their neighbor's closet to kill Olivia. However, it is impossible to think that Jenny would not have heard Ghostface on the phone inside her own closet, especially when he screamed.
Major Plot hole: In the span of 15 years, the small city of Woodsboro witnesses its second instance of a successful and bloody serial killer. The last time, dozens of people were murdered, including cops, before the killers could be stopped by Sidney Prescott herself. But now that the killing cycle is coming back....... the City Mayor or the Sheriff do not call for help from the state police or FBI or anyone else to help them out.
The same conditions that made it possible for a murderer with a knife to go on a killing spree is kept intact yet again. It was shown before that Woodsboro only has a few police officers and thus cannot protect all its citizens from a prepared serial killer. It is already contrived in the first movie that no outside authority is involved, but with the fourth movie, it is completely mind-boggling.
Major Plot hole: Sidney's cousin, Jill, is revealed to be the mastermind and main killer of the movie. Her plan was to take Sydney's place as the surviving victim and become famous herself. She had a great plan that was probably created over weeks if not months. The final act of her plan was to kill Sydney......so.......she stabs her in the stomach......once.
During the whole movie, she kills people by stabbing them MULTIPLE times in their backs and chests because she knew that it wasn't enough to kill them with only 1 blow. But obviously, when she has to kill Sydney and knows the cops will be arriving soon, she stabs her only once in the stomach and is then surprised to learn Sydney was saved by doctors.
Major Plot hole: Characters in the movie are aware that horror movies exists. They know the clichés and how dangerous it is to go around places all alone. But even when a new killer shows up and transforms their fictional knowledge of survival into a real asset, most of them still go around alone at night while their friends were killed in the past few hours. They sure make it a lot easier for the killer !
Plot contrivance: All the people living in Woodsboro are crazy. Their town is best known has one of the most creepy city to live in. It is a small community where almost 20 people were killed in the most horrific ways. Yet, the citizens love it ! They have festivals celebrating the killers and the deaths they brought with them. Even more surprisingly......the festival CONTINUES even when a new killer shows up and killed 3 teenagers in the past 2 days. How is that even remotely possible ? Kirby even witnessed her best friend died a couple of feet away from her, and yet she is HAPPY to go to the Staboton instead of being hiding in her basement crying her life out.
Plot contrivance: After Sidney witnesses Olivia dying in the house next to her (the second murder scene), she runs after the killer with no weapon. What was her plan exactly ? She saw the young girl die so she knew she could not save her, and she saw that the murderer had a knife.....but she goes running towards him without any weapon. You would think that after 3 serial killers wanting to kill her she would have a gun or something.
Unaddressed Issue: Where are the parents of all those teenagers ? Are they all past victims of Ghostface ? Because most of the characters in the movie are teenagers who live inside big houses without any parents in sight. To continue on this line of thought: where were all the doctors at the hospital in the final showdown? Yes it was at night, but there was no staff around in the corridors and rooms - it was a complete ghost hospital right until the villain died.