She is a wicked witch with magical spells that are capable of doing anything, even going as far as death. She also enjoys rhyming, which really annoys Grunty's three sisters, also they really dislike her rhymes. Grunty also keeps her spells in a book named Cheato, who doesn't enjoy Grunty's plan of becoming beautiful and decides to help Banjo and Kazooie.
In Banjo-Kazooie, Grunty kidnaps Banjo's sister Tooty and plans to steal her beauty so she can be the most beautiful woman in all of Spiral Mountain. If you get a Game Over then her plan suceeds.
Two months later in Grunty's Revenge she inhabits a robotic form of herself called Mecha-Grunty, and plots to prevent Banjo and Kazooie from ever meeting.
Two years later, in Banjo-Tooie her sisters Mingella and Blobbelda join her in an attempt to restore Grunty to her former body.