The Simpsons: Every Treehouse Of Horror Ranked Worst To Best
7. VII. The Thing And I; The Genesis Tub; Citizen Kang
In the grand history of one-time supporting characters, Bart's "evil" brother Hugo ranks pretty damn high (though he's not really canon, unfortunately). He turned up in The Thing And I, confined to the attic and fed solely on buckets of fish heads, before one of The Simpsons' greatest ever twists reveals Bart's actually the evil twin. As if anyone was surprised. It's a really strong compartmental story and it's loved for good reason.
The Genesis Tub meanwhile isn't quite the usual horror fare of the early days, but it's another strong story from before cameos and silliness distracted too much. And it even survives being a Lisa episode, so that's no bad thing.
And then there's Citizen Kang, which gets away with being a Kang and Kodos episode thanks to some excellent political satire and some top class Homer ineptness when he kills Al Gore and Bill Clinton by accident. The culture clash of the alien body-snatchers holding hands as Gore and Clinton is just lovely.