5. Scorpion Replacement (Star Trek: Voyager)
We know Scorpion as the end of third season/fourth season opener for Star Trek: Voyager which introduced Seven of Nine. But that wasn't the original plan for the two parter. Instead, the first idea which was placed on the drawing board featured the return of the duplicate Voyager crew from the episode Demon. It would have seen "Voyager" return home to the Alpha Quadrant, either pulling past Deep Space Nine or arriving at Earth amid much celebration and fan fair. A number of ideas were put forward, which differed on whether the duplications knew who they were or thought they were the original versions. But the writers couldn't get their heads around it and it was shelved - but not entirely cancelled. It was later re-considered for the slots which ended up being used for both Year of Hell and The Killing Game. It was finally considers for the end of season four and start of season five. The idea ended up being ditched in the end because it was felt that it would undercut the series when the real crew managed to get home. In the end, the alternative crew did reappear, but no-where near Earth - instead they were completely wiped out when they returned in the episode Course: Oblivion.