Madelyn shares the same looks as her sister, but their personalities are somewhat different. For example, Madelyn seems more extroverted, while Velma is more introverted.
Her nickname in high school was "Doe Eyes Dinkley" according to Shaggy. Velma mentioned briefly that Madelyn had been in clown college for a semester.
DTV: Scooby-Doo! Abracadabra-Doo