E.T. II: Nocturnal Fears

ET II: Nocturnal Fears was a planned sequel film to Steven Spielberg's ET from 1982, with script written by himself and Melissa Mathison.

Plot
The film was supposed to have Elliott and his friends being kidnapped by extraterrestrial villains, and ET would have to save them.

Why It Was Cancelled
Steven Spielberg then said such a sequel would rob the original film of its virginity, and the project was cancelled.

Result

 * The film was permanently cancelled.