Factual error: The part of the play Sidney stars in begins with "All, behold the dreaded fate of Troy, that once stood proud and light upon the hills of Sparta." Please, what? There is a correlation between Sparta and Troy (the bride of the king of Sparta ran off with the prince of Troy, that was the casus belli), but phrased this way it does not make sense. (00:57:00)
Other mistake: The movie is supposed to happen "a couple years" after the previous (words of the moviegoer behind Jada Pinkett) but the current date shown at the theater says 1997, and Scream was set in September 1996 (calendar at Stu's house distinctly visible when he brings Sid's dad out of the closet).
Audio problem: Randy is leaving class to meet Sidney, but his classmate first asks him "So, Mr. Originality..." The camera cuts away before she finishes the sentence, but you can tell that the word that came after "So" doesn't match what the actress is saying. (00:17:20)
Answer: His main motive was fame, or infamy for that matter.