9. The Praying Mantis Eggs
The fourth episode of the first season involves a giant praying mantis disguised as an attractive biology teacher. Xander develops a crush on her, and before long, he has to be rescued by Buffy and the gang.
It’s a pretty dumb storyline, all things considered, and in the final shot of the episode, the camera drops down to reveal a cluster of praying mantis eggs inside the biology classroom. You would assume, therefore, that there’s going to be some kind of follow-up episode.
But there isn't. The murderous offspring of a giant praying mantis are never addressed again. Did they fail to hatch? Did someone destroy the eggs? Are there more praying mantises roaming around somewhere?
Turns out we’ll never know. The cliffhanger at the end of the episode has no payoff whatsoever. Still, this is probably a good thing given the praying mantis is one of the worst villains in the show.