Star Trek: 10 Alien Races That Only Appeared Once
5. "Conspiracy" Aliens
How can you discuss one shot aliens without probably the biggest missed opportunity of them all?
The creatures from The Next Generation's first season instalment, Conspiracy, confirmed the show could deliver quality and danger in one satisfying package.
Conspiracy depicted the first big (internal) threat to Starfleet and the Federation of this era and contains some genuinely chilling moments. Lunch is a bit more lively than Riker and Picard were expecting for one and then there's the graphic, exploding Dexter Remmick under intense phaser fire after he's chewed up a stop-motion bug. Even with that, these aliens mark a big step away from what fans of Kirk, Spock and McCoy might have expected and tested the waters for other threats on the horizon.
The penultimate episode of that first season even ends with a signal sent out into the depths of space, teasing that we might see them again. Non-canon works since have speculated that the aliens featured were an "evil" offshoot of the Trill, since they seem to inhabit bipeds in a similar way but this has never been borne out on the screen. Good theory though.