Grumblebum Thrashers are mutant creatures found in Mudwater Hollow. It is unknown if they are supposed to look deformed or its just the murky water of Mudwater Hollow affecting them. Their method of attacking is a single slash from their spatula.
- They are listed in the Greebles section in the BradyGames Strategy Guide of Skylanders: Swap Force.
- A friendly Grumblebum named Bad Breath appears in Skylanders Academy, though while he resembles a Grumblebum Thrasher, he is much shorter, as well as missing their extra eye and tree branch horns.