Continuity mistake: When Stanley is in jail, he put toilet papers on the toilet seat. But a few seconds later the toilet paper is not on the toilet.
Audio problem: When Tina is tied to the palm tree with the bomb armed and Ipkiss is fighting with the goons. Ipkiss fights with Dorian and punches him over and over with Dorain on his back. The punching sounds are VERY obviously off from the action.
Continuity mistake: The "loaner" car Stanley picks up at the mechanics is a 1951 Studebaker Champion. However, the car that falls apart on the bridge is a 1950 Studebaker Commander.
Revealing mistake: When the super-stretch limo is pulling up to the club, we see window after window go by, then the picture cuts for a moment to the crowd watching. Upon returning to the limo shot, the edge of the front door can be seen on the left side of the screen, ruining the illusion of the ridiculously long limo.
Continuity mistake: When Dorian arrives at the Coco Bongo Club at the end of the movie, he smashes the doors which end up on the floor, but when the fight is over and everybody is leaving the club, the doors are back on the doorframe.
Continuity mistake: After Stanley found the mask and gets back home and is watching some cartoons, Milo wants him to throw the frisbee. When the camera is switching from Stanley to Milo and then back to Stanley again you'll see the remote move to the right.
Continuity mistake: When Dorian dismisses his charges to capture the Mask for 50,000.00, Tina and Dorian chat. She is about to light her cigarette but doesn't. In the next cut away there is smoke in the air but she still hasn't lit it yet. As the scene continues you only see smoke when Diaz has her back to the camera.
Continuity mistake: When Stanley is doing the Cuban dance watch his legs. Whenever the camera is behind him you can see him wearing black kneepads but when the camera is in front they aren't there.
Continuity mistake: In the bar scene at the end of the movie Stanley dives over the bar while Dorian's thugs shoot at him, when they stop shooting you see one of the thugs drop the magazine out of the gun then the scene cuts away from him and when it cuts back you see the thug drop the magazine out of the gun again.
Factual error: In the first scene of the movie, a diver is underwater, and he is talking to someone on the radio. How can he talk, when he is biting down on the mouthpiece from his scuba tanks? And his mouth is obviously not moving.
Continuity mistake: During the musical number "Cuban Pete", Jim Carrey's blue shirt is sometimes tucked in and sometimes is not.
Continuity mistake: When The Mask paints the flush handle, near the end of the movie, watch the far left hand side when it shows Tina and The Mask. The Mask is shutting a door on the tree where the flush handle really is.
Revealing mistake: When The Mask is dancing with Tina and he turns her into a human tornado while spinning her around, none of the onlookers in the crowd show the slightest bit of amazement at the impossible feat that just occurred in front of them, indicating that the extras were not directed to react to the special effects.
Visible crew/equipment: Towards the end of the film you see the long haired baddie grab Milo by the hind legs (just before Milo puts the mask on). As Milo starts to change you can just about see the baddie who is holding his legs, except he is now a different person with brown curly hair, nobody who is seen prior or following this shot. Presumably he is the dog trainer.
Continuity mistake: When Tina kicks the mask out of Dorian's hand and Milo leaps through the air to catch it, he catches it with his mouth at the mask's chin, yet when he lands the mask has been turned round so the chin end is now facing the ground.