The oversized teeth on the Mask character were originally to be used only during silent scenes, but Jim Carrey learned to talk while wearing them to make his character that much more wacky.
Chuck Russell revealed that a lot of money was saved on special effects after Jim Carrey was cast. Carrey's body movements were so flexible and cartoonish, they didn't see the need to enhance them digitally.
The producers hated the Cuban Pete musical number and wanted it gone. They insisted that it was too long, not funny and dragged, but test audiences loved it so much that they kept it in.
The banana-yellow suit that Jim Carrey wears is based on a suit which his mother made for him for his first attempt at stand-up comedy.
The part when Stanley is being chased by the gangsters and pulls the wet condom out of his pocket and says, "Sorry, wrong pocket," was improvised by Jim Carrey.