(at around 58 mins) Cindy has blood on her clothes that comes from nowhere (the source is revealed in a deleted scene).
(at around 51 mins) During the skeleton chase, the "KILL HER" sign on Cindy's back disappears instantly when she runs into Shorty.
(at around 34 mins) When Cindy is fighting with the cat one minute the litter box is full, then the next minute the litter box is empty as the cat flings kitty litter at Cindy.
(at around 14 mins) When Cindy is driving to Hell House, exterior shots of the car show her driving along fenced fields, but interior side views within the car show her driving through what appears to be a mountain pass.
(at around 54 mins) When Cindy, Brenda and Buddy reunite after being chased by the skeleton, Hugh Kane gives Buddy a wedgie and Buddy has white underwear. But when Cindy and Buddy are trapped in the science room, and when Buddy unzips his pants his underwear is green.
(at around 49 mins) The characters use thermo goggles that detect body heat to find the ghost. Which doesn't make sense because he is already dead and wouldn't produce body heat.
(at around 27 mins) The costumes change during the spoof of the Nike commercial where the characters are in the costumes they are supposed to be in the next day. However, this is probably deliberate.
As this is a spoof, the emphasis is on laughs. Strict continuity with the original Scary Movie (2000) is not necessary. The movie is allowed to stand on its own terms.
(at around 1h) When Cindy is pleasuring Buddy with her hand, at the climax, he pushes his hips up. For a split second, you can see that his pants are fully on and zippered.
(at around 9 mins) When Shorty and Cindy are doing left and right punches, some guys walking in the background disappear halfway across the screen.
(at around 17 mins) When Hanson is getting ready to show Cindy her room, he takes her bag of clothes and it spills open. The clothes that end up on the floor actually fall from above Hanson, not from the bag itself.
(at around 55 mins) When Alex chases "Huey", he throws furniture at her and then drops a chandelier on her. A dummy of her can briefly be seen before the chandelier smashes into her.
(at around 1h 3 mins) When Dwight is falling from outside the window, you can see his paralyzed legs flailing and kicking.
(at around 45 mins) the lower part of David Cross's (Dwight) hair piece comes unstuck from his head and folds back, revealing the lace base. By the end of the scene this lower part of the hair piece has completely fallen off.
Although Professor Oldman says the class is for people with sleep disorders. There is a joke that Shorty is asleep and drooling. In reality these are symptoms of a sleep disorder called "Idiopathic Hypersomnia". A disorder in which a person sleeps so much, that they experience debilitating symptoms causing perpetual fatigue throughout their day.
In the exterior footage, the mansion is shown to have a recessed from doors. However, after Cindy enters the house, it's revealed the front doors are actually extended from the house and the interior front hall even has windows that don't exist on the exterior.
(at around 23 mins) When Hanson enters the dining room area to serve dinner, a crewmember's hand is visible stopping the door from slamming.
An odd bulge in the sleeve makes the presence of the robotic device that controls Hanson's mutated hand obvious. As well, the sleeve of that arm is clearly empty, indicating that the actor's real arm is tucked under his clothes, perhaps even controlling the robotic hand.
(at around 1h 14 mins) When Cindy is at the hotdog stand with Hanson we see the remote/battery pack for her mic on her back. When she turns, we see the mic wire running up to her shirt (this has been fixed in the DVD release).
(at around 52 mins) When Cindy is being chased by a skeleton, as it turns a corner you can see a skateboard device attached to the feet to help it move (this has been fixed in the DVD release).
(at 1h 8 min) When Brenda is knocked down by the butler, you can see a loading symbol on her in the last frame.