The Incredibly Stupid Swamp Monster (voiced by Frank Welker) is a minor ally of the U.S. Acres gang, who nickname him Swampy. He was originally a robot created by Dr. Karloffis Boar before walking into a swamp, thus becoming a swamp monster. As his name suggests, he has very little intelligence, getting multiple facts wrong and finding incredible ways to hide. He also has a tendency to be quite affectionate.
- The musical theme for Swampy is a banjo being tuned.
- Swampy's affection for certain animals is similar to that of Hugo the Abominable Snowman from Looney Tunes. Coincidentally, Frank Welker has occasionally voiced Hugo in modern features.