Arthur Loses His Marbles & Friday the 13th

Arthur Loses His Marbles: Muffy's new marbles prompt Arthur and his friends to start playing marbles. Arthur signs up for a marbles tournament after he gets trained by Grandma Thora. When he discovers that he has to compete against Grandma Thora in the marbles tournament, he plays poorly on purpose but Grandma Thora loses first when she finds out what is happening.
Friday the 13th: Brain does not believe in superstitions and goes on to try to prove this by doing things superstitiously believed to bring bad luck, like breaking a mirror. Counter to his hypothesis, a streak of bad luck strikes. When the Brain believes he ultimately disproves superstitions by turning around a baseball game they are sure to lose, his friends believe he has some lucky objects.