In a photograph in Dylan's flat, we can see him and his assistant masked as Groucho Marx. In another scene, we can see that Dylan keeps his weapons stashed in a safe behind a Duck Soup (1933) poster (a Marx brothers movie). Both are references to the Dylan Dog comics on which this movie is loosely based on. Although in the comics, Dylan's assistant, sidekick and comical relief is not the zombie from the movie, but a stage actor who looks exactly like Groucho Marx, calls himself Groucho, and always dresses and behaves like the legendary comedian (it's implied this is due to the character's slight insanity).
In the comics, Dylan Dog's sidekick is a Groucho Marx impersonator who goes by the name Groucho and behaves exactly like the comedian, having lost all recollection of his true identity. This had to be changed for the film, due to legal issues related to the use of Groucho's likeness.
In the comic book Dylan drives a white convertible Volkswagen Beetle with a black roof. In the movie it is a black convertible Volkswagen Beetle with a white roof.
This is the second film Brandon Routh and Sam Huntington have collaborated on, with the first being Superman Returns (2006).