The Simpsons Halloween Special X (Season 11; Oct. 31, 1999)
Amazon; Disney+; Halloween Specials Wiki; Halloween Wiki; IMDb; Simpsons Wiki; TV Tropes; Wikipedia

Intro: Kang and Kodos are hosting the tenth anniversary Halloween special. Then there's a couch gag with the Simpsons watching the special on TV, and an amusing callback to last year's special.

I Know What You Diddly-Iddly-Did: In a parody of I Know What You Did Last Summer, Marge accidentally hits and kills Ned Flanders with her car. Homer tries to cover up how Ned died, but there's a twist ending.

Desperately Xeeking Xena: An accident with an X-ray machine the police are using to examine Halloween candy gives Lisa and Bart super powers. They become Clobber Girl and Stretch Dude. When a villain called the Collector (Comic Book Guy) abducts Lucy Lawless (aka Xena: Warrior Princess) from a convention, Stretch Dude and Clobber Girl come to her rescue... or try to.

Life's a Glitch, and Then You Die: Homer failed to prepare the power plant's computers for Y2K, and the errors that caused spread all over the world, leading to mass chaos and destruction. Eventually, the Earth is evacuated with two rocket ships, but there's a twist that put me in mind of a plot point from The Restaurant at the End of the Universe.