1. “Conspiracy” – Star Trek: The Next Generation
An alien parasite is taking over members of Starfleet, with the intent of taking over through a covert invasion. The general premise isn’t exactly the scariest thing ever, as Romulans have long tried to sneak into other alien governments in disguise in an attempt to take over from within (or destabilize). Yet, this episode featured a far more spooky version of that concept.
Instead of Romulans undergoing surgery to present differently, these aliens work their way into the human body and take over control. Fans of the Animorph series will be very familiar with this premise. Again, the idea isn’t too out there, in fact, we saw Khan Noonien Singh do similar things during the events of Star Trek II: The Wrath of Khan.
No, what makes this episode so perfect for Halloween is the absurd and gruesome body horror that the produces allowed to be put into the show. Not only does the climax feature a giant parasite alien emerging from the abdomen of a Starfleet officer, but you also get to see the human head get melted down to the bone, like in Raiders of the Lost Ark.
The alien debuting its real form in the busted open stomach of a former officer of Starfleet remains one of the grossest and out-there moments in all of Star Trek.