S2·E7 City on the Edge of Forever (Flashbacks)

While their school bus is dangling on the edge of a cliff, the boys remember some of their past adventures. Mrs. Crabtree catches a ride into town with a stranger and winds up doing a brief stint as a standup comedienne. Back in South Park, Mr. Mackey convinces the parents that their missing children must have run away. In the end it's all a dream within a dream.