She is a cantankerous old woman with a New York accent. She is a gray squirrel, usually wearing a green hat decorated with a white gardenia and black purse and rainbow umbrella that she occasionally uses to hit other characters. She lives in a hollow tree with her nephew Skippy Squirrel, despite their polar opposite personalities, who loves to hear her tell stories about her former days of stardom. While Skippy represents a cuter style of cartoon characters, Slappy is a more chaotic and old-school character, enjoying violence for comedy's sake and resentful of milquetoast, censor-influenced modern cartoons.
She first appeared in Animaniacs' third episode, "Slappy Goes Walnuts", originally aired on September 15, 1993.