Looney Tunes: Back in Action (2003) – Trivia – IMDb

John Cleese made a brief cameo in the film at one point during the Paris sequence, but his cameo was cut out, because it didn’t have anything to do with the film. Also, the reason Scooby-Doo and Shaggy make cameos in the film, even though they are not Looney Tunes, was because Joe Dante wanted some non-Warner Bros. characters in the film like Tom & Jerry, and Droopy, but Warner Bros. thought that would be too weird, so they told him a Scooby-Doo cameo would seem more “appropriate”. If one looks closely, the animation of Scooby and Shaggy is stiffer, and more limited than that of the Looney Tunes characters, referring to the drastically cheaper budgets of the Hanna-Barbera studio, at the time the original Scooby series was created.