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.
The Mask (1994)
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Directed by: Chuck Russell
Starring: Cameron Diaz, Jim Carrey, Peter Riegert, Amy Yasbeck, Peter Greene
Continuity mistake: When Stanley is in jail, he put toilet papers on the toilet seat. After Milo gets inside the jail cell, the toilet paper is not on the toilet anymore. (01:10:35 - 01:13:10)
Trivia: The Mask is based off the Dark Horse Comic of the same name. The only difference is that Dark Horse Comics carry a lot of dark tones in their comics. When Chuck Russell was directing The Mask, it was supposed to be set in that way. When Jim Carrey was given the role of Stanley Ipkiss, it was turned into a comedy.
Question: Why would he have to steal the money from the bank? Given everything else he makes.
Answer: While under the influence of the mask, Stanley repeatedly gets revenge on people that have wronged him. The Mask wouldn't even need to create money out of thin air to get into the club since he could just use his powers to get in, so since he feels that he is mistreated at the bank, he robs it.
Answer: Nothing he makes while The Mask is permanent, and when separated from him reverts or disappears, as we see with the piece of pajama. If he made money, for example to get into the club, then immediately after giving it to the people and walking inside, it would vanish, probably causing him then to be thrown out. As Phaneron said, in addition, by robbing the bank to get it, he also strikes back at one of those he feels mistreats him.