She was said to have hidden a special treasure somewhere on Sesame Street long before the present day, only Oscar was never able to find the rumored map. Charlie finds it in one of Yucky Mama's old books, depicting the street from around 1969. The magic map allows Yucky Mama to communicate with the treasure-seekers (Oscar, Elmo, Abby, Nina, and Charlie) and instruct them on how to find her treasure, which involves visiting three landmarks and doing a grouchy challenge at each one.
Due to the map's age, the since-removed landmarks are all lost on the modern residents of the street, save for Oscar. He guides them to each one as they complete each challenge. Eventually, they find Yucky Mama's hidden treasure concealed within an exterior wall of 123 Sesame Street. The treasure is a can that magically spring-loads trash all over the street.