Scooby-Doo 3

Scooby-Doo 3: Monster Mayhem' was a planned sequel to Scooby-Doo 2: Monsters Unleashed that was set to be the third installment in the live-action Scooby-Doo'' film series.

Plot
Unknown

Why It Was Cancelled

 * 1) Scooby-Doo 2 failed at the box office and both live-action Scooby-Doo films were panned by critics and fans alike.
 * 2) Joseph Barbera died a few years after Scooby-Doo 2 was released in theaters.

Result

 * 1) The film was cancelled for good.