The Really Rottens are a Laff-a-Lympics team led by Mumbly. The two other teams are the Yogi Yahooeys and the Scooby Doobies. Unlike the other two teams of the Laff-A-Lympics, the Really Rottens did not appear in any other Hanna-Barbera produced show, but they were similar in style to several villainous characters from earlier Hanna-Barbera shows.
- Mumbly (team captain) - Similar to Muttley. He starred as a detective in his own series of shorts, as part of the Tom and Jerry/Grape Ape/Mumbly Show, and he appeared along with Dread Baron in Yogi Bear and the Magical Flight of the Spruce Goose.
- Dread Baron - Similar to Dick Dastardly. He was a WW1 era pilot, and took his name from the pre-production main character of Dastardly and Muttley in Their Flying Machines, called "Stop That Pigeon".
- Daisy Mayhem - A female hillbilly with superhuman strength. She has no likeness in any other H-B production.
- Sooey Pig - Daisy's sidekick, a giant, sloppy pig. He also has no likeness in any other H-B production.
- Great Fondoo - A villainous stage magician. He is a character originally created for this show with a design by Iwao Takamoto, suggesting that he comes from the same stock as the villains frequently opposed by Scooby-Doo and Dynomutt. Allegedly, he was repurposed from Abner K. Dabra, the villain in a 1963 Yogi Bear storybook.
- Magic Rabbit - The great Fondoo's sidekick. He frequently speaks only one word, "Blech."
- Dastardly Dalton - Originally from The Huckleberry Hound Show. The Dalton family were a group of dastardly outlaws who were mentioned in the short "Lawman Huck" but never appeared together on screen until the first episode of Laff-a-Lympics. They would later star alongside Huck again in The Good, the Bad and Huckleberry Hound Dastardly is the leader of the trio. Short and temperamental.
- Dirty Dalton - The middle member of the Dalton family. Looks similarto Dastardly, but with curly blond hair.
- Dinky Dalton - The ironically named largest of the Daltons. He was the only one of the trio to appear on The Huckleberry Hound Show, as the oversized outlaw Huck had to arrest in the short "Lawman Huck".
- Mr. Creeply - A monstrous gentleman, with the stature and temperament of Peter Lorre. Similar to Weirdly Gruesome of the Gruesomes.
- Mrs. Creeply - Mr. Creeply's wife, similar to Creepella of the Gruesomes.
- Junior Creeply - Mr. Creepley's son, similar to Gobby of the Gruesomes.
- Orful Octopus - The Gruesomes' pet octopus. Similar to Occy of the Gruesomes.