Treehouse of Horror Series

Breakdown
Treehouse of Horror episodes typically consist of four parts: an opening and Halloween-themed version of the credits, followed by three segments. These segments usually have a horror, science fiction or fantasy theme and quite often are parodies of films, novels, plays, television shows, Twilight Zone episodes, or old issues of EC Comics. Although they are sometimes connected by "wraparounds", the three segments rarely have any kind of continuing connection within the episode. The exception is "Treehouse of Horror V", in which Groundskeeper Willie is killed by an axe in a similar fashion in all three segments. The episodes are considered to be non-canon and always take place outside the normal continuity of the show. From "Treehouse of Horror" to "Treehouse of Horror XIII", all three segments were written by different writers. In some cases there was a fourth writer who wrote the opening and wraparound segments. For the original "Treehouse of Horror", there were three different directors for the episode. Starting with season 15's "Treehouse of Horror XIV", however, only one writer has been credited with writing each Treehouse of Horror episode. On occasion, the episodes will be used to showcase special animation, such as the "Treehouse of Horror VI" segment "Homer3", in which a computer-animated Homer is shown in a non-animated setting. "Treehouse of Horror XX" included the segment "There's No Business Like Moe Business", which was the first to be musically-themed.

Reception and Legacy
The Treehouse of Horror episodes are often among the top-rated episodes of their season and many of the Treehouse of Horrors have generally been well-received by fans. However, like The Simpsons itself, critics have noted a decline in the quality of the later episodes. In its first airing, "Treehouse of Horror" finished with a 15.7 Nielsen rating and a 25% audience share and would lose to The Cosby Show. It was said that it "set a level of excellence that viewers never expected creator Matt Groening to repeat", although it was also described as "kind of stupid and unsatisfying". "Treehouse of Horror V" is considered the best episode by several critics: it finished ninth on  Entertainment Weekly' s top 25 The Simpsons episode list, fifth on AskMen.com's "Top 10: Simpsons Episodes" list, and was named best episode of the sixth season by IGN.com. In 2006, James Earl Jones, who guest starred in "Treehouse of Horror" and "Treehouse of Horror V" was named seventh on IGN's "Top 25 Simpsons Guest Appearances" list.

In 2006 IGN.com published a list of the top ten Treehouse of Horror segments, and they placed "The Shinning" from "Treehouse of Horror V" at the top, saying it was "not only a standout installment of the annual Halloween episode, but of The Simpsons, period." Rounding out the list were "Dial "Z" for Zombies", "The Devil and Homer Simpson", "Time and Punishment", "Hungry Are the Damned", "Clown Without Pity", "Citizen Kang", "If I Only Had a Brain", "Bart Simpson's Dracula" and "Starship Poopers". The third, fourth and fifth episodes were each represented by two segments. The most recent episode on the list was "Treehouse of Horror IX", which first aired in 1998.

"Treehouse of Horror VII" is Simpsons creator Matt Groening's seventh favorite episode, and the line he likes best is "We have reached the limit of what rectal probing can teach us." "King Homer" of "Treehouse of Horror III" is one of Matt Groening's favorite segments. "Treehouse of Horror III" is also noted for the moment where Homer shoots Ned Flanders and Bart says "Dad, you killed the Zombie Flanders!" only for Homer to reply, "He was a zombie?" It is also one of Groening's favorite lines.

Awards
In 1996, the "Homer³" segment of "Treehouse of Horror VI" was awarded the Ottawa International Animation Festival grand prize. In 1998, "Treehouse of Horror VIII" won a Golden Reel Award for "Best Sound Editing – Television Animated Specials"; the recipients were Robert Mackston, Travis Powers, Norm MacLeod and Terry Greene. Bob Beecher also received a nomination for "Best Sound Editing in Television Animation – Music" for "Treehouse of Horror X".

The second, third, fifth, eighth, ninth, fourteenth and fifteenth and eighteenth Treehouse of Horror episodes were nominated for "Outstanding Individual Achievement in Music Composition for a Series (Dramatic Underscore)" at the Primetime Emmy Awards. The second and third "Treehouse of Horror" episodes were also nominated for "Outstanding Individual Achievement in Sound Mixing for a Comedy Series or a Special". In 1996, "Treehouse of Horror VI" was submitted for the Primetime Emmy Award in the "Outstanding Animated Program (For Programming less than One Hour)" category because it had a 3D animation sequence, which the staff felt would have given it the edge.[46] The episode failed to win and Bill Oakley later expressed regret about submitting the episode.

In 2013 "Treehouse of Horror XXIII" was nominated for the Primetime Emmy Award in the "Outstanding Animated Program (for Programming Less Than One Hour)" category.

Merchandise
There has been a variety of merchandise based on the Treehouse of Horror episodes, including books, action figures, comic books, video games, DVDs and a "Treehouse of Horror" version of Hasbro's board game Monopoly. Although every Treehouse of Horror episode until "Treehouse of Horror XV" has been released along with its season in a boxset, in 2003, The Simpsons: Treehouse of Horror DVD was released. It includes Treehouse of Horrors V, VI, VII and XII.[51] A Treehouse of Horror comic book has been published annually since 1995, and collected into several books, including The Simpsons Treehouse of Horror Fun-Filled Frightfest, Bart Simpson's Treehouse of Horror Spine-Tingling Spooktacular, Bart Simpson's Treehouse of Horror Heebie-Jeebie Hullabaloo and The Simpsons Treehouse of Horror Hoodoo Voodoo Brouhaha. Several video games based on The Simpsons include levels with a Halloween theme, including The Simpsons: Hit & Run and The Simpsons Game. In 2001, Fox Interactive and THQ released The Simpsons: Night of the Living Treehouse of Horror on Game Boy Color. The entire game has a Halloween theme as the player tries to save the Simpson family from the Treehouse of Horror.