3. The Aliens (Conspiracy - The Next Generation)
One of the ultimate alien races never to appear anywhere else in any other episode of Star Trek perhaps? There were a few hints earlier in the first season of The Next Generation that things weren't all well in the higher echelons of Starfleet but it took until this episode to see what all the fuss was about. What an appearance it was though aliens infiltrating Starfleet and not doing such a bad job on all fronts. Who can you trust? What are these things and what is their ultimate goal? Not that we ever find out, but we do get one of the goriest scenes in the franchise when Remmick ends up eating phaser. For those who don't know, the original UK BBC TV version had that shot nicely snipped out. Hence a great reason to stick a pic of it here (and in HD quality). Had they returned I reckon their "major" villain status would have been assured, however the signal that beams out across space as the credits blink up never was checked out. According to non-canon material these buggy little critters were a nastier version of the Trill. But as they were, they were a great creation that should have got more time on screen and presented an interesting if short lived threat to the Alpha Quadrant who can you trust? Just check for a little quill on the neck before you answer that question.