Trivia: The trivia and in jokes abound in this film. Firstly, you have Janet Leigh (Jamie Lee Curtis' mother) playing Norma (reference to Psycho) and complaining that the "showers are blocked again" (second reference to Psycho). In her last scene in the film, Janet Leigh is about to get into and drive away in the same car that she used in Psycho.
Trivia: Late in the film, before Laurie/Keri goes back inside to battle Michael alone, she tells John and Molly to "drive down the street to the Becker's". This is a reference to "Scream," in which Casey Becker's father told her mother to go "down the street to the Makenzie's", a line included in the original Halloween.
Trivia: Early on in production, this was intended to be the final "Halloween" film, with director Steve Miner and star Jamie Lee Curtis wanting to give the series a definitive ending in which Laurie triumphs over the "boogeyman" Michael Myers. Shortly before filming began, one of the producers exercised a clause in his contract for the series and informed Miner and Curtis that he would not allow them to kill off the Michael Myers character. Both Miner and Curtis nearly left the project, with Curtis in particular voicing her disdain over the decision. But eventually both chose to stay on, with Curtis reasoning that as far as her character Laurie was concerned, she kills the "real" Michael Myers in the end. Curtis only appeared in the following film "Resurrection" out of a begrudging respect for the series, wanting to give the character a proper send-off. Curtis has subsequently stated that 2018's "Halloween," a direct sequel to the original that ignores every other sequel including "H20" and "Resurrection," felt like a much more appropriate way to bring her character back into the "Halloween" universe, and is her preferred follow-up to the original.
Trivia: One of the biggest hurdles of the film? Oddly enough, it was choosing the right design for the mask. Director Steve Miner originally wanted a more stylized, paper-white mask and several scenes were shot with this original design. However, the producers felt the mask didn't look right and wasn't menacing enough, and thus the design was changed into one based more around the look of the mask from the previous film ("The Curse of Michael Myers") and included more detail and shading. Director Miner protested, but his attempts to go with his first design were vetoed. Nevertheless, the original mask can occasionally be seen in the film for some scenes they didn't want to reshoot (mainly sequences with Michael in the distance), and in some of the trailers.
Trivia: Not a mistake, just something to notice: When the guidance counselor is checking on Molly and Sarah, they are watching Scream 2, the scene where Cici (Sarah Michelle Gellar) gets killed. As he enters the room and says their names, watch the TV. As he says "Sarah", Sarah Michelle Gellar turns around.
Trivia: Originally composer John Ottman wrote an entirely different score for the film - one that was more whimsical and less traditional. The producers panicked at the last minute, feeling much of the score didn't work for the film, and had to bring on fellow composer Marco Beltrami to write new music to fill in the gaps. Unfortunately, due to the limited time, Beltrami could only write minimal original music for the film, and thus cues from some of his other scores (notably "Scream" and "Mimic") were recycled and reused in the film.
Trivia: In the first movie, Laurie sees Myers while she is looking through a window during school. The teacher surprises her by asking her a question and her answer is about fate. When she looks back out the window Myers is gone. In H20 Molly is looking out a window during school, she sees Myers, Laurie asks her a question and her answer is about fate. When she looks back out the window Myers is gone.
Trivia: If you look past the nurse when she goes next door to where the two boys live and knocks on the door before asking them to check her house, you can see the fat cenobite with the sunglasses from the first two Hellraiser films sitting on the bench on the porch. It's just a mannequin, but it does look impressively detailed.
Trivia: When the film opens with the 50s tune "Mr. Sandman" over the soundtrack, it's not just a simple reminder of 'Halloween II', but a signal that this film is continuing from 'Halloween II' rather than its immediate predecessor 'Halloween: The Curse of Michael Myers'. As "Mr. Sandman" was the last thing heard before 'Halloween II's closing credits, 'Halloween H20' in effect picks up where 'Halloween II' left off.