Gunn began his career in filmmaking with Troma Entertainment in 1995, for which he wrote the independent film Tromeo and Juliet. Working alongside his mentor Lloyd Kaufman, the co-founder of Troma, Gunn learned how to write screenplays, produce films, scout locations, direct actors, distribute films, and create his own poster art. After contributing to several other Troma films, Gunn in 2000 wrote, produced and performed in the superhero comedy The Specials, directed by Craig Mazin and featuring Rob Lowe, Thomas Haden Church, Paget Brewster, Judy Greer and Jamie Kennedy.