Mary Lou was a popular girl in her school and is actively defying authority and sleeping with boys and using them to her own devices. She thinks only for herself and her dream of being Prom Queen. On Prom Night at Hamilton High, 1957, Mary attends with a rich boy named Billy Nordham, who gives her a ring with her initials on it. When he goes to get punch, he catches her making out with another boy named Buddy Cooper. Mary admits to using him and he storms off, before deciding to get revenge by dropping a stink bomb, he acquired from the bathroom on her. When Mary Lou is elected Prom Queen, she walks onto the stage, while Billy drops the bomb from the catwalk. To his and everyone else horror, the bomb ignites in her dress, burning her alive. As Mary Lou dies, she glares at Billy, realizing he's the one who killed her.
Hello Mary Lou: Prom Night 2Edit
In 1987, Vicki Carpenter goes looking for a prom dress at School, and finds a trunk containing Mary Lou's prom accessories, unwittingly unleashing Mary Lou's vengeful spirit. Vicki's best friend Jess Browning arrives, and when she's alone, Jess takes a jewel out of Mary Lou's crown, and is murdered in cold blood by the vengeful spirit. Her death is deemed a suicide, due to her being pregnant. After Jess' death, Vicki has constant nightmares about Mary Lou, and suffers hellish hallucinations. She goes to Buddy Cooper, who is now a local priest. Buddy realizes the presence of Mary Lou's vengeful spirit/ghost, when his Bible burst into flames. Buddy goes to find Billy (Michael Ironside), who is now the principal of Hamilton High, and the father of Vicki's boyfriend, Craig. Buddy's warnings fall to deaf ears, as Billy refuses to believe the story. When Mary makes Vicki hallucinate herself in Vicki's rival, Kelly Hennenlotter, Vicki slaps Kelly. In detention, in another hellish nightmare, Vicki is dragged into a liquid chalkboard and emerges, possessed by Mary Lou. During the possession, Mary Lou visits and mercilessly kills Buddy in cold blood by stabbing him with a miniature crucifix. She later kills and slaughters Vicki's other friend Monica Waters in the locker room without showing any remorse. Mary also seduces Craig and knocks him out. She goes to Billy's house to taunt him and reveal her identity to him. Billy gets a gun after taking his son home, fearing Mary Lou will get revenge on him for killing her back in the past through his son and knocks him out. While Mary Lou is getting ready for prom, she tries to seduce Vicki's father Mr. Carpenter and kills her mother Mrs. Carpenter. The prom, Mary Lou enjoys the festivities, while Kelly, who wants to be queen, preforms an oral sex on Joshua, who is running the votes. Mary Lou mercilessly electrocutes Joshua and rigs herself as Prom Queen. Craig arrives trying to stop his father from shooting Vicki, but is too late. He reaches to the apparently dying Vicki who transforms into the charred demonic corpse of Mary Lou herself, which heals back to her living self but still has some burn scars. In the chaos, Kelly is killed by a falling light fixture and Craig is chased into the prop room. A portal to the underworld opens, and tries to suck Craig in, but Billy puts the crown in Mary Lou's head, apparently appeasing her spirit/ghost, thus releasing Vicki. With Mary Lou gone, Vicki and Craig get into Billy's car with Billy. Billy is suddenly wearing Mary's wig before driving off with Craig and Vicki, implying that he is possessed by her ghost.
- She shares the same abilities as Carrie White.
- Like Mystique\Raven Darkholme, she takes form of any humans by mimicking their voices.