Muttley is sometimes confused with the crime-fighting dog Mumbly from The Mumbly Cartoon Show.. Mumbly looked similar to Muttley. They had a similar laugh. But, their ears were different and Mumbly had blue fur and wore a trenchcoat. Mumbly later showed up as the captain of the villainous Really Rottens in Laff-a-Lympics along with his accomplice, "The Dread Baron," who resembles Dick Dastardly. The Dread Baron and Mumbly later appeared in the TV movie Yogi Bear and the Magical Flight of the Spruce Goose. It is not certain why Mumbly was retconned as a villain, neither is it certain why he and Dread Baron were apparently used as substitutes for Dastardly and Muttley, especially in the Yogi Bear movie where Paul Winchell voiced the Baron instead of Dastardly (and in the scene where the Baron's crashed plane is shown, it's Dick's plane from Dastardly and Muttley in Their Flying Machines, complete with the "D" on the side). Not to mention that in that story Mumbly had once utilized his tail to fly just like Muttley does in Dastardly and Muttley in Their Flying Machines. The reason most suggested is that the Wacky Races characters (including Dastardly and Muttley) were not fully owned by Hanna-Barbera as the show was a co-production with Heatter-Quigley Productions.
An early version of the Muttley/Mumbly character appears in the 1964 Hanna-Barbera feature film Hey There, It's Yogi Bear!. This prototype Muttley ("Mugger") is a mean-spirited dog with a travelling circus who has a penchant for biting his owners on the leg. The character may also have been inspired by the Atom Ant show's "Precious Pupp" who was known for laughing the same way. Muttley and his master returned in the Wacky Races video game with Billy West voicing the dog