15. The Cosby Show, Season 6 (NBC; September 24, 1989 - May 3, 1990)
Raven-Symoné joined the cast of The Cosby Show as Olivia when bossman Bill decided the child actors were getting too old. Thus, an element of cuteness had to be injected back into the show. The writers took the directive a bit too far, though, and Olivia-centric episodes turned the show's overall tone distinctly sachhrine.
The addition of the pint-sized actress marked the beginning of a tough period for the show that would see the persistent addition of new characters as the series moved towards its inevitable conclusion. The Cosby Show went on to call it quits after season 8.