Simpsons Season 11, Episode 4: Treehouse of Horror X

Season 11's annual trio of Halloween stories.

I Know What You Diddily-Iddily Did – Marge accidentally kills Ned Flanders and is haunted by claims that someone knows what she did.
Desperately Xeeking Xena – Bart and Lisa gain super powers after a freak accident and must save Lucy Lawless from the Collector
Life's A Glitch, Then You Die – When the Y2K bug causes everything electronic and computer generated in the world to go haywire, the family searches for a way out.