Mary Ann Smith is a minor villain from The Powerpuff Girls. She appears in the episodes "Supper Villain" and its sequel "Just Desserts".
Mary Ann is the girls' next-door neighbor. She is the wife of Harold Smith and the mother of Bud and Julie. Mary Ann is initially a seemingly innocent homemaker. She is very perky, cheerful, effervescent, and vivacious. She loves to cook and bake - she makes pancakes for breakfast every morning. However, she also has a bossy and shrewish side, and she is often the one yelling at her husband for not doing evil things.
In "Supper Villain", Mary Ann invites the Powerpuff Girls and the Professor over for dinner. She is aware of Harold's bathroom time, which he is using for making his villain costume, and tells him to not mess up the dinner. She initially gets along with the Powerpuff Girls...until dinner.
The girls watch Harold carefully, since he has a sinister plan to melt the Professor's head. At dessert, Mary Ann serves everyone coconut cream pie, which everyone ends up throwing at each other in a food fight. When the police come and arrest Harold, the Powerpuff Girls and the Professor leave. Mary Ann then swears revenge against the girls.
In "Just Desserts," Harold comes home to find that Mary Ann, his soon-to-be henchwoman, has a sinister plan of her own - she is planning to destroy the Powerpuff Girls. Bud and Julie join in as well. She has prepared villain costumes for her and her children, which everyone dresses in. Mary Ann then reveals her changes to the family car - she has equipped it with weapons. She then tells of her and Harold's plan to destroy the Powerpuff Girls' home.
When the Powerpuff Girls come home from grocery shopping, they find that the Smiths had wrecked their home. Mary Ann decides to go over and see the girls' reaction. She pretends to be sympathetic and protective, but when the girls are glad that nobody was hurt, she runs away. Mary Ann tells her family to get in the car.
Under Mary Ann's command, Harold drives the car into the girls' home and the family chases them until the girls destroy the car. They ask why are the Smiths doing this. Mary Ann responds, saying that they tried to be good neighbors, but the girls drove her husband insane, got him arrested, and ruined her dinner. The girls decide that that's not a good reason at all, and beat the Smiths up. Mary Ann and the rest of her family go to jail.