Granny Grim is the grandmother of The Grim Reaper. Like her grandson and the rest of her family, Granny Grim is an 'undead, talking magical skeleton' and has dreadlocks growing out of her skull. Also like her grandson, Granny Grim speaks in a Jamaican accent.
Granny Grim is the mother to either one of Grim's parents, and the mother-in-law to the other. Granny Grim may also possibly be the sister of Kali, Grim's great aunt--but the relation is never verified in the series run, only by the virtue of their relation to Grim.
Granny Grim was first seen in Billy's Growth Spurt, when, after Billy had gorged himself into a 'junk food coma', Mandy asked Grim if he knew of a cure for 'Toxic Junk Food Syndrome'. Grim thinks of his "Granny Grim's" remedy that will expel all of the toxins within Billy's body. First, however, they needed to track down an important ingredient for the remedy, an Underworld species of flowers found in inter-dimensional bogs--the "Screaming Meemee". After Granny Grim's remedy for Toxic Junk Food Syndrome had successfuly expelled all of the toxins in Billy's body as a growth called "Yaap yaap" that later detatched itself from Billy, Granny Grim provided Grim and Mandy with the follow-up remedy, "Heebee-Geebee Juice" to revert Yub-Yub back to the unhealthy additives, preservatives and fatty acids that it came from.
Granny Grim is seen later in One Crazy Summoner: After receiving a call through the toilet from Nigel Planter at Grim's sugestion for a Love Potion that was guaranted to work, Granny Grim is washed up onto the beach where Grim, Billy, Mandy and Nigel were located, confused as to how she had ended up there when the last thing she knew she had been talking to her toilet, before she was washed back after Nigel thanked her for the Love Potion. Granny Grim was washed up again later for chocolates that could 'win' Nigel the heart of his school's most popular girl, before being washed back home commenting that she should just stop talking to her toilet.
Granny Grim is seen again, in Nergal's Pizza, where Grim, in competion with Nergal over the superior recipe for a pizza, enlists the help of his "dear old Granny Grim" for her excellent recipe for pizza.