High Quality Content by WIKIPEDIA articles! "Treehouse of Horror X" is the fourth episode of The Simpsons` eleventh season, and the tenth annual Treehouse of Horror episode, consisting of three self-contained segments. It first aired on the Fox network in the United States on Halloween 1999. In "I Know What You Diddily-Iddily-Did", the Simpsons cover up a murder and are haunted by an unseen witness. In "Desperately Xeeking Xena", Bart and Lisa gain superpowers and must rescue Xena star Lucy Lawless from the Comic Book Guy`s alter ego The Collector, and in "Life`s a Glitch, Then You Die", Homer causes worldwide destruction thanks to the Y2K virus.