The original pug from Men in Black (1997) was used to play Frank again, but since the pug was now seven years older, they used makeup to hide the gray fur around its nose.
Famke Janssen was originally cast as Serleena, and even completed some of the filming, but was forced to drop out of the project due to a death in her family. Lara Flynn Boyle was then cast in her place.
In an interview with Will Smith and Tommy Lee Jones, Smith said: "It was great working with Frank the Pug in the first film, but since we came back he's been acting like an a-hole." Jones then said, "Yeah, Frank's had a bit of an identity crisis since the neutering."
Though Linda Fiorentino's character (Laurel the medical examiner at the morgue) was prepped to appear in the sequel alongside Will Smith, it has been reported that Tommy Lee Jones only agreed to return under the direct stipulation that Fiorentino wasn't invited back. The reason was left unclear but tabloids reported it was due to her tempestuous nature. Jones has never confirmed it and Fiorentino has never denied his accusations.
Linda Fiorentino was originally intended to reprise her role as Agent L, before eventually being dropped from the script.