* CompleteMonster: Mary Lou Maloney, from here and [[Film/PromNightIIITheLastKiss the following film]], was a popular, if [[AlphaBitch spiteful and manipulative girl]] in life, but became something much, much worse in death. When she used two boys, Buddy and Billy to become prom queen, and is killed in a [[DeadlyPrank revenge prank gone wrong]], Mary's spirit awakens years later, killing a pregnant teenager named Jess and [[DemonicPossession possessing]] her friend Vicki, trapping the latter in a dark world. Mary Lou seeks to become prom queen again, killing everyone who gets in her way; this includes Buddy, now a priest; Vicki's friend Monica; and attempts to seduce Vicki's father in his daughter's body before killing her mother. Mary Lou learns Vicki is now dating Billy's son Craig, and seeks revenge on Billy through his son. Billy is forced to shoot Vicki, causing Mary Lou's spirit to manifest and go on a rampage, during which she attempts to drag Craig into the underworld. When seemingly defeated, Mary Lou possesses Billy with the apparent intent to try to kill Vicki and Craig again. Escaping hell, Mary Lou kills another one of her ex-boyfriends before seducing and becoming obsessed with a student named Alex. Mary Lou would go on to kill students and teachers for Alex before he rejects her. In retaliation, Mary Lou kills his best friend Shane, framing Alex for the deed and plans on killing his girlfriend Sarah. At the prom, Mary Lou agrees to let Sarah live if Alex agrees to be her prom king for eternity in Hell. When Sarah seemingly rescues Alex, Mary Lou kills Sarah before leaving Alex stranded in Hell.
* EvilIsSexy: Mary Lou, an attractive (both in her original body and [[spoiler:Vicki's]]), promiscuous DepravedBisexual who gets a full frontal scene [[spoiler:while riding around in Vicki's body and trying to seduce Monica in the shower.]]
* {{Narm}}: [[spoiler:Mary Lou!]]Vicki singing "Tutti Frutti" as [[spoiler:she telekinetically crushes Monica in the locker.]]
* NightmareFuel: High points include Jesse's incredibly violent death, the locker room scene, and that rocking horse with its fucking tongue.
* SurprisinglyImprovedSequel: Although it can [[InNameOnly barely be called a sequel]], and the first still has a following, ''Hello Mary Lou'' manages to be much scarier, better-acted, and less boring than the first. It also takes itself less seriously, and has more fun with its ridiculous premise.