According to Warwick Davis, the movie was originally planned as a scary kid's film, but the studio thought it would work better as a more adult horror, so inserts were filmed to increase the gore and violence.
One scene required the Leprechaun to find and eat Lucky Charms cereal, which the company gave them permission to do. Upon seeing the finished film, the company was displeased and would not allow them to use the scene. The film makers had the choice to either cut the scene or to re-shoot it, costing them more money. They chose to re-shoot it, replacing the brand name with an obvious spoof of the name brand cereal, and, made one last additional surprise ending scene while they were filming. Furious with the cereal company for making them re-shoot the scene, they pulled the kid character aside and had him say a new line. His line, "Your luck just ran out!" was changed to "Fuck you, Lucky Charms!" as an obvious reference to the whole ordeal.