Episode Title:Arthur Loses His Marbles / Friday the 13th.Episode Description:Arthur Loses His Marbles: Muffy's new marbles prompt Arthur and his friends to start playing in a marbles tournament. Arthur is trained by Grandma Thora, a former professional marbles player herself, but when he discovers that he has to compete against Thora in the marbles tournament, he plays poorly on purpose. Thora forfeits when she finds out what is happening.
Friday the 13th: Brain does not believe in superstitions and tries to prove his hypothesis by doing things superstitiously believed to bring bad luck, like walking under a ladder, stepping on a crack, and destroying a mirror. Counter to his hypothesis, a streak of bad luck strikes. Brain goes to Buster to get lucky charms, but during a baseball game on Friday the 13th, Brain forgets the charms and hits a home run that wins his team the game, proving his hypothesis.