It all started when Jillian, Katie, Amanda, and their friend Harrison go to see the amazing Jimmy 'O James. While Slappy is preforming on stage with Jimmy, Mary-Ellen sees her true love for the first time. That is when she fell in love with him so Mary-Ellen while Harrison, Katy, Amanda, and Jillian have been asked up on stage and Jimmy asks for their address and sends Slappy to their house. Mary-Ellen, during a birthday party, brings Slappy to life by saying the magic words in Slappy's pocket. Well the story goes on, until the final battle between Mary-Ellen and Slappy. They fight, because Slappy did not actually love Mary-Ellen, as everyone thought. He really loves Jillian. They both die when Slappy turns on a buzz saw and tosses Mary-Ellen into it, but she grabs him and they both get cut into pieces.
Slappy is brought to life by Jimmy 'O James, instead of Mary-Ellen. He offered Jimmy an "offer he couldn't refuse." That offer was to be Slappy's slave, and also having Jimmy act as if he were a ventriloquist in a show starring Slappy. He was already alive when Harrison, Jillian, and Katie went there to see the show. Instead of Mary-Ellen staring at Slappy, Slappy was staring at her (actually, he was staring at Katy).
Mary-Ellen thought that he was staring at her and had fallen in love with him. After the show, Katie loses Marry-Ellen and Jillian goes back-stage to look for her. She stumbles upon Jimmy seemingly arguing with Slappy (later found out that Slappy was talking Jimmy into giving him to the family of his 'bride') Much later, Jillian and Katie are running away from Slappy, when Mary-Ellen reveals herself to be alive after Jillian calls her a "dumb doll." Mary-Ellen replied, "Who are you calling dumb, ugly!", causing Jillian to drop her. Slappy comes in through the basement window. Now, they are both trapped by both Mary-Ellen AND Slappy.
Slappy tells them he stole their mother's ring for the special occasion, making Mary-Ellen reply,"Oh Slappy! You say the nicest things!" Slappy then replies, "What? I don't want you cheap piece of plastic!" slapping Mary-Ellen across the face, then completing his sentence saying, "I want her!" pointing at Katy. Mary-Ellen gets furious and starts attacking Slappy. They fight on the basement stairs. Jillian notices him near the saw switch and turns on the light. But Slappy's head (which was shoved down by Mary Ellen) rises and clicks on the saw. He says: "You guy's cut me up! ha ha!" killing them both. We then see Slappy and Mary-Ellen's ghosts float out of their ruined bodies and disappear. Their parents then come home and the two children tell them that Harrison was locked in the bathroom. They unlock it with a spare key, but Slappy has possessed Harrison. Mary Ellen seems to have disappeared.
Mary-Ellen is short, with rosy cheeks and a malicious smile. She has purple eyes and black hair with white streaks dyed in it, usually tied in a bun, similar to the Bride of Frankenstein. She has quite a ruddy complexion and a Shirley Temple nose. She also wears a white dress with a pink sash tied around her waist. In the episode, she is blonde and wears a white dress.