Played by: Sofia Coppola
Not even trying to hide his nepotism, Francis Ford Coppola cast his daughter, Sofia, as Mary Corleone in The Godfather Part III, and the results were horrifying. The character's conflict with her father (Al Pacino), and creepy romance with her cousin (Andy Garcia), was supposed to be the emotional driving force of the film. However, Coppola brought such a stiff, wooden performance to the role that you can’t help but hate her by the end.
This is an example of one wrong casting decision affecting an entire film. Her lack of believability as an actress made Mary a frustrating character to watch. In turn, it made the entire movie frustrating to watch, and a huge letdown after two phenomenal films. Rival mob families couldn’t bring down the Corleone’s, but some amateur acting sure did.