Mary-Biff is Biff's baby daughter who appears in a 1989 episode of Sesame Street. She is revealed as one of Biff's four children, and bears a family resemblance to her father (mainly through the prominent nose).

Biff offers child-rearing advice to Luis (mainly teaching counting and the alphabet), and Maria brings back Mary-Biff, so her dad can demonstrate his third piece of advice: showing that you love your kids.