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.
Revealing mistake: When Kellaway shows up at Stanley's apartment to question him about his pajamas and Stanley scrambles to stuff all the stolen bank money into his closet, you can see that a few of the bills are blank on the back side, revealing that the money is a fake movie prop.
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. (01:10:35 - 01:13:10)
Continuity mistake: When Stanley wakes up after his second night as the Mask, he is holding the mask. In the next shot, the mask has moved further up onto the pillow and Stanley isn't even touching it.
Revealing mistake: When Milo is trying to jump up to the jail cell, the brick wall is not brick but plastic as can be heard from his paws scratching on it. (01:11:35)
Continuity mistake: When The Mask is being frisked at the park the cops find a picture. Kellaway holds it with one hand, but in the following shot he is holding it with both.
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. (01:17:20 - 01:28:05)
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. (00:58:20)
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.
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. (00:00:40)
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. (00:15:45)
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. (01:25:20)
Revealing mistake: When The Mask dances with Tina for the first time, after he swings her around the floor you can see the stunt double's face, older than Cameron Diaz.
Continuity mistake: In the club when Carrey is being shot by the goons when he's behind the counter, he jumps over the counter. Just before he jumps on the counter, you can see those were two separate takes. Pay close attention to the head on the left. (01:25:30)
Continuity mistake: During the musical number "Cuban Pete", Jim Carrey's blue shirt is sometimes tucked in and sometimes is not. (00:58:20)
Revealing mistake: In the alley, The Mask tells one of the street thugs that he's going to pull his underwear over his head. Here you can see that The Mask's rubber 'skin' is peeling up on the back of his neck.
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.
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.
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. (01:23:15)
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.
Chosen answer: It's an old car, so obviously a numbr of things could be wrong with it, like the clutch or the engine. Faults with either of these things would cause a car to brake in this way.