Mrs. Doolin is an elderly lady that's subject to rumor, and said to be a ghost. She made her debut sole appearance "Who Killed Who". She is voiced by Betty White.
After excluding Mandy from their board game Who Killed Who? (a Clue type of game) for being a girl, Billy and Irwin mistakenly throw their dice into the backyard of a haunted house. Grim warns them about the ghost of Mrs. Doolin, a lady that lived there. Mandy dares to go inside to retrieve the dice. Once inside the house, she befriends Mrs. Doolin, who is alive and well. Mandy tells her that "somebody" (meaning Grim) "told me a story that you fed the bones of some kid to your pet spider and that you're really a ghost". Mrs. Doolin looks puzzled at first, but then begins laughing for a bit. Then she tells Mandy that all the stories told about her (that anything that went beyond her fence into her garden never came back) are inventions from Grim, whom she beat a long time ago in a staring contest.
Fearing for Mandy's life, Billy also ventures into the house, but Mrs. Doolin and Mandy scare him away by posing as ghosts. However, it appears that Mrs. Doolin is in fact a ghost, and when she meant "beating Grim", it meant that she had "beaten death".
- (about Grim) You must’ve been talking to that old bag of bones, Grim. Ever since I beat him in a staring contest, he’s been making up all kinds of stuff about me. In fact, he’s never really forgiven me for beating him in just about everything.