Continuity mistake: When the killer rips his mask off to expose his face to Maggie, his eyes go from brown to yellow between shots. It is explained later that his yellow eyes becomes brown thanks to colored contact lenses, but the killer does not remove any contacts when rips off his mask.
Continuity mistake: As the giant mosquito flies toward Mr. Davis, Davis has the remote control which controls the mosquito hanging around his neck. In the very next shot the remote control has disappeared.
Continuity mistake: When "Tina" ties up Bud in his wheelchair, she puts a belt around his body. The belt shifts/rotates around his body between shots (you can tell by a patch on the belt, which moves around).
Revealing mistake: When the killer is putting masks on in front of Maggie, you can see the dead body of Tina hanging behind Maggie. The dead body moves / shakes / breathes many times throughout the scene.
Audio problem: When Mark says to Maggie "No disguise looks that real that close up," Maggie replies "Maybe," but her mouth says something else.
Continuity mistake: When The Possessor puts a mask of Toby on, in front of Maggie, he then takes it off and puts it on a metal tray. He then takes a second mask and puts it on. then, when he goes to put the second mask down, the mask of Toby, which he left on the tray, is now placed on a foam dummy head.
Visible crew/equipment: After Maggie sells The Possessor a ticket, she realizes who it was, and runs out of the ticket booth and over to Tina, and speaks with her quickly. As Maggie speaks with her and then goes off, reflected in the glass is a crew member/cameraman in a red t-shirt.
Continuity mistake: When the letters fly off of the movie theater sign, they land all around Suzanne, scattered all over the floor. However when she walks over to the box office, to collect the ticket, the letters are nowhere to be seen on the floor.
Plot hole: When Toby is checking everyone to make sure their costumes work, wheelchair-bound Bud is shown standing in a coffin-fixture. Since he was in the coffin costume, there was nothing there to be "holding" the character in a standing position, and he was obviously not in his wheelchair, as he is at standing height with everyone else.
Continuity mistake: When "Tina" places the tape recorder down in front of Bud, the black strap on the tape recorder is on the left side in one shot, but in the next shot it is on the right side.
Continuity mistake: When 'Tina' is attacking Bud, she puts tape over his mouth. In one close-up, the bottom of the tape is folded up, revealing the bottom half of his mouth, but in the subsequent wide-shot, the tape is perfectly neat, and unfolded, covering the whole of his mouth.
Visible crew/equipment: In the montage, where the group are getting Dreamland prepared for the Horrorthon, in one shot we see Bud fiddling with the electronic box (which is unplugged). As the camera pans backwards, you can see the shadow of a crew-members head wearing headphones, cast on the electronic box.
Other mistake: When Tobey's unmasked in front of Maggie he's badly burned. Yet his hands appear to be perfectly okay contradicting his claim of losing most of the flesh on his body. Surely they'd be scarred up too.