Billy, and Stu

Stu: Stu is a deeply psychotic and maniacal yet dimwitted person. Although had no distinctive motive for helping Billy murder people, he nonetheless takes joy in it, proving himself to be extensively sadistic. Adding to his sadism, Stu is rather spiteful as he also saw this as a good opportunity to get revenge on his ex-girlfriend, Casey Becker by killing her and Steve Orth purely out of pettiness for her dumping him. Stu also likes to put on a playful and joking demeanor to hide his true deathly, sadistic, frigid cold-blooded, and cruel nature.

Even after his true nature is revealed, Stu shows more of his cruelty by continuing to crack jokes to taunt Sidney. He shows intense joy in planning to frame her father for the killings and even gets ecstatic as him and Billy prepare to stab each other to make themselves look like victims.

Billy: Billy is a narcissistic, sociopathic, monstrous and psychotic teenager who often pretends to love Sidney just as a cover for his true intentions; to mercilessly kill her and her parents. He is a manipulative and heartless monster who wants to inflict his emotional crisis onto other people and let his anger and rage all out with no remorse at all. He enjoys killing others and has no emotions or empathy at all. He even said that living in a horror film is fantastic, and therefore, his ultimate goal is to turn his life into a horror movie so he won't feel any pain after what he did and how he should one day pay a high price.