Other mistake: After Billy Loomis and Stuart "Stu" Macher are revealed as the villains, they stab each other multiple times to appear as victims. Billy cuts Stu too deep, and Stu begins feeling weak and bleeding profusely from his wounds, showing that he may be dying. When Sidney (in the Ghostface costume) stabs Billy with the umbrella, Stu's rage takes over and he suddenly has the dangerous energy to battle Sidney in the living room. Stu nearly kills Sidney, until she pushes the TV on his head. If Stu was dying in the kitchen, how does he have all that energy to fight Sidney?
Other mistake: During Tatum's murder we see some problems exacerbate. The killers are not supposed to be invulnerable and are wearing a cheap costume, but they receive hard hits (Tatum breaks two bottles of beer, one straight to the face) and they don't have a single scratch. When she is killed, nobody hears her scream and nobody else needed to grab a beer either. Furthermore, Ghostface has the garage door fully open, but without knowing who is on the other side, that is one room away from the others, goes by the mysteriously unlocked door to the inside of the house. And we see Billy (who should be the killer there, since Stu was at the party) join in coming from outside.
Other mistake: When Stu brings Sidney's dad out in the kitchen, you can see behind him a September 1996 calendar. Earlier in the movie, the scenes inside Principal Arthur Himbry's office do show a September calendar, which is obviously the intent of the movie, but it's a September 1997 calendar.
Other mistake: Randy answers the phone and receives the news that the principal has been killed and left to hang from the goalpost. He gets the call from the telephone by the TV, and he his head reaches about half the height of the TV. The hidden camera is on top of the VHS player, a shelf underneath the TV, but somewhat Gale and Kenny in the TV truck get a close-up of his mouth. (01:16:00)