No one else has uploaded ALL The Simpsons - Treehouse Of Horror Specials (1-20) as Single Links, Especially on both RS and MU except for me, that is only why I put a site name in the links. Enjoy all of these. Took me all day to upload them so please say thanks.

Screenshots of each episode under each episode description.

Season 2 Episode 3: Treehouse Of Horror I
In the backyard treehouse on Halloween, Bart and Lisa try to frighten each other by telling three scary stories.
Bad Dream House:
The family moves into a new house and eerie things begin to happen.
Hungry Are The Damned:
The Simpsons are abducted by aliens, Kang and Kodos, who seem to have plans on eating the family.
The Raven:
Lisa reads the classic Edgar Allen Poe poem.
Season 3 Episode 7: Treehouse Of Horror II
After eating piles and piles of Halloween candy, Bart, Lisa and Homer have nightmares that haunt them all night.
The Monkey's Paw:
Lisa dreams that the family goes on a trip to Morocco and buys a cursed monkey paw that grants its owner four wishes. By wishing for world peace, Lisa accidentally paves the way for an alien invasion by Kang and Kodos, who enslave the human race.
The Bart Zone:
Bart's dream, in which he has the power to read minds and affect a person with his thoughts.
If I Only Had A Brain:
Homer dreams that Mr. Burns steals his brain for a giant robot he's building. Due to an accident, Mr. Smithers is forced to sew Mr. Burns' head onto Homer's body.
Season 4 Episode 5: Treehouse Of Horror III
The Simpsons gather for a Halloween party and exchange ghost stories.
Clown Without Pity:
In the first tale, told by Lisa, for his birthday, Homer buys Bart a talking Krusty doll with a few glitches: It tries to kill Homer with a knife and strangle him to death. No one believes that the doll is really trying to kill Homer until the doll attempts to drown him in the dog dish.
King Homer:
In the next story, told by Grandpa, Homer plays King Kong to Marge's Fay Wray. Mr. Burns plays a maniacal millionaire who plunders the jungle in search of mythical giant gorilla. The gorilla falls in love with the millionaire's beautiful assistant and carries her to the first few floors of the Empire State building.
Dial "Z" For Zombies:
Finally, Bart tells a story in which he casts a spell from a book of witchcraft and accidentally brings Springfield's dead to life. The only thing that can send them back to their graves is the right spell.
Season 5 Episode 5: Treehouse Of Horror IV
With a Night Gallery style opening, Bart introduces three tales.
The Devil And Homer Simpson:
Homer falls asleep, while Carl and Lenny eat all the doughnuts. When he realizes that all the nearest doughnuts are gone, he sells his soul for a doughnut. The devil comes up and signs a contract with him, causing more mischief than Homer thought.
Terror At 5 1/2 Feet:
Bart dreams about his death on the school bus, and later realizes, that his dream is starting to become real when he is the only one to see a gremlin taking down the bus piece by piece. Nobody sees it except for him, so he tries to get it off.
Bart Simpson's Dracula:
Mr. Burns is a vampire and Bart falls victim to his bite, Lisa convinces the rest of the family they must go to his castle and put an end to the curse.
Season 6 Episode 6: Treehouse Of Horror V:
The Shinning:
The family becomes caretakers of an estate in the mountains owned by Mr. Burns, where he cuts the cable and takes out all beer, which leads Homer to insanity.
Time and Punishment:
Homer fixes the toaster and it becomes a time machine. While visiting the past, he kills a bug, which affects the future in a big way. When he tries to fix the time line, he breaks it again.
Nightmare Cafeteria:
Principal Skinner finds a solution to his overcrowding problem and the quality of meat in the cafeteria: eating the students.
Season 7 Episode 6: Treehouse Of Horror VI
Attack of the 50 Foot Eyesores:
Strange atmospheric conditions bring giant advertising statues to life. The Lard Lad is furious at Homer for taking his doughnut, so he, along with all the others, begin destroying the town of Springfield.
Nightmare on Evergreen Terrace:
Willy's death, due to disinterested parents, causes him to come back into the dreams of their children, where he kills them, resulting in their deaths in reality.
Homer3:
Homer finds a strange area in the house behind the bookcase. When he steps through, Homer becomes trapped in a three-dimensional universe.
Season 8 Episode 1: Treehouse Of Horror VII
The Thing and I:
Homer and Marge warn the children not to go up into the attic. Of course they do and there they discover Bart's Siamese twin, who plans to sew them back together.
The Genesis Tub:
Lisa's science experiment becomes a quickly-developing micro-universe, where she is thought of as God and Bart is the devil.
Citizen Kang:
Homer is abducted by Kang and Kodos. The aliens take Homer to Washington where they replace Clinton and Dole just in time for the election. Homer tries to explain the truth, but no one believes him.
Season 9 Episode 4: Treehouse Of Horror VIII
The Homega Man:
Quimby insults the French government who launch a neutron bomb in retaliation at Springfield. Homer escapes the blast and begins enjoying himself in seemingly deserted town.
Fly vs. Fly:
The family visits Prof. Frink's yard sale. Homer purchases a matter transporter. Bart uses it in an attempt to become "Superfly", with comic and near disastrous results.
Easy-Bake Coven:
In 1649, Marge is accused of being a witch. It turns out she and her sisters actually are witches who learn that it's easy to scare people into giving them treats.
Season 10 Episode 4: Treehouse Of Horror IX
Hell Toupée:
It's his third strike, Snake is sent to the electric chair. He vows revenge on all on those who were there when he was caught, Apu, Moe & Bart. Snake is electrocuted and his organs are saved for transplant. The beneficiary of his hair is one Homer J. Simpson. The hair begins exacting the revenge promised by its former owner.
The Terror of Tiny Toon:
Marge takes the batteries from the TV remote control. Bart substitutes plutonium with strange results as he and Lisa become cartoon characters in an episode of Itchy & Scratchy, where the violence is real.
Starship Poopers:
When Maggie gets her first tooth, a fang, and loses her legs, which are replaced by tentacles. Marge confesses that Homer is not the father, but rather Kang is. To settle the dispute on what would be better for Maggie's future, Bart suggests they go on The Jerry Springer Show and of course a fight or two breaks out.
Season 11 Episode 4: Treehouse Of Horror X
I Know What You Diddily-Iddly-Did:
The family (with Marge driving) runs over and believes that they've killed Ned Flanders. After covering up their misdeed, the family is haunted by someone who knows what they diddily-iddly-did, Ned Flanders himself.
Desperately Xeeking Xena:
Lisa and Bart are blasted with radiation, get superpowers and become "Stretch Dude and Clobber Girl". In the episode "Enter...The Collector", they must stop Comic Book Guy (a.k.a. "The Collector") who has kidnapped Xena to add his collection.
Life's a Glitch, Then You Die:
Homer is the nuclear plant's Y2K compliance officer. His negligence causes the Y2K bug to get out and spread across the networks of the world, causing mass destruction. Causing the government's "Operation Exodus" program to be activated, taking the best and brightest off the Earth to a new civilization on Mars.
Season 12 Episode 1: Treehouse Of Horror XI
G-G-Ghost D-D-Dad:
Homer dies because he's eaten the deadliest plant on Earth, broccoli. When he arrives at the Pearly Gates of Heaven he finds he cannot get in because he hasn't done one good deed all his life. St. Peter gives him 24 hours to perform at least one deed.
Scary Tales Can Come True:
Bart and Lisa are abandoned to the deep dark woods. With a book of Fairy Tales to guide them, the pair navigates their way past a troll and three bears eventually arriving at the house of the witch who lives in the gingerbread house. Meanwhile, Homer and Marge change their minds and he goes in search of the children giving Rapunzel a haircut along the way.
Night of the Dolphin:
Lisa lets a dolphin go free but it turns out this particular dolphin is the dolphin's king. Now that he has his freedom he plots to take his revenge on the land dwelling humans.
Season 13 Episode 1: Treehouse Of Horror XII
Hex And The City:
The family sees a gypsy, but Homer's usual ineptitude causes the gypsy to seek her revenge by cursing him and his loved ones. In an effort to get the curse lifted, Homer catches a leprechaun and releases it upon the gypsy with surprising results.
House Of Whacks:
The family home obtains an upgrade, the Ultrahouse 3000, a computer that will do everything for them. Everything is going great until the house falls in love with Marge and tries killing Homer.
Wiz Kids:
Bart and Lisa are attending wizard school. The evil Lord Montymort and Slithers have designs on capturing Lisa, so that Montymort can take her essence. They use Bart's rivalry with his sister as the means to get at her.
Season 14 Episode 1: Treehouse Of Horror XIII
The Simpson family, along with Ned Flanders, holds a séance which brings the ghost of Maude Flanders back from the grave. With her presence in the room, she opens a book which brings us three haunting tales.
Send in the Clones:
Homer finds that his new hammock is capable of making clones, and he begins making and using the clones to do all of his chores.
The Right to Keep and Scare Harms:
Lisa finds the grave of William Bonney who was killed by gun violence. In his memory, she starts a gun control crusade, which makes Springfield totally gun-free; even the police no longer have guns. Now defenseless, the corpse of William "Billy the Kid" Bonney and his cohorts rise from the dead and start raising havoc in town.
The Island of Dr. Hibbert:
The family takes a trip to "The Island of Lost Souls," where they find Dr. Hibbert is running the island's resort. Marge thinks that something creepy is going on there, but when she goes off to investigate she is captured by Dr. Hibbert who turns her into a cat woman. Homer goes in search of a cure for Marge's condition and encounters Ned Flanders (who needs to be milked). Flanders takes Homer to meet the others who've been converted into beasts.
Season 15 Episode 1: Treehouse Of Horror XIV
Reaper Madness:
Death comes to the door of the Simpson home looking for Bart. A la a Benny Hill chase the family tries to elude Death. Homer kills Death and suddenly the world is without death. No one can die. Homer puts on Death's robe and suddenly finds himself "The Grim Reaper." He starts doing the job until he has to kill Marge. He gets out of the reaper job by pleading with God, but then he "pulls a fast one" on him by substituting Patty's body for Marge.
Frinkenstein:
Homer gets a call telling him that he's won the Nobel Prize, only the call is really for Professor Frink. So that his father might partake in the awards ceremony, Professor Frink reanimates his father's corpse. His father's corpse escapes and goes on a killing spree to collect some replacement body parts.
Stop the World, I Want to Goof Off:
Bart and Milhouse get hold of a stopwatch that actually allows them to stop time. They are having a great "time" and almost get away with it, until they are outsmarted by the mayor. On their run from the angry mob, the watch breaks and they are the only two moving in a world where time has stopped.
Season 16 Episode 1: Treehouse Of Horror XV
We open with an episode of "Keepin' It Kodos" with Kang. In this episode, Kang and Kodos have the Simpson family for dinner with their boss. The meal is a success as Kang gets a hyper-galactic promotion.
The Ned Zone:
Homer knocks Ned unconscious with his bowling ball, when he recovers he discovers that he was really dying of a brain tumour & the bowling ball lodged it out (which give him premonitions of doom). He tells Homer about his new power and Homer wants to know his future. Ned sees Homer being shot in the back, and the shooter is he.
Four Beheadings and a Funeral:
The "Mutton Chop Murderer" has taken another victim, and Eliza Simpson and her sidekick Dr. Bartley join with Inspector Wiggum of Scotland Yard to find the killer. The dagger used is the latest crime is found to be one of a set, and they find that the set was owned by C. Ebenezer Burns. They go to the opium den and find that Burns had sold the daggers to a fat man (Homer) to get money for opium. The fat man is caught and sentenced to death, but when Eliza and Dr. Bartley find yet another body, Eliza knows the fat man is innocent and finds an important clue to the real killer's identity on the latest murder weapon.
In the Belly of the Boss:
At the "New Invention Expo" Maggie gets inside of a new vitamin pill that is going to be reduced by Prof. Frink's new shrink ray. The pill is swallowed by Mr. Burns. The other Simpson family members become bionauts inside a submarine that is miniaturized and sent inside of Mr. Burn's body. Maggie is found, but there is not enough power to get everyone and the submarine out of the body, someone must stay behind.
Season 17 Episode 4: Treehouse Of Horror XVI
It is game six of the World Series and Kang and Kodos decide to speed up the play of the game and they fire the acceleray. They shatter the fabric of the universe and everything is destroyed.
B.I.: Bartificial Intelligence:
Bart falls into a deep coma from which he will never emerge. Well Bart does wakes from his coma only to find that his family has replaced him with David, a newly developed artificial robot son.
Survival of the Fattest:
Homer and others are invited by Mr. Burns to his estate for “A Most Dangerous Game.” It turns out that they are participants on “The World Series of Manslaughter” featuring guest analyst Terry Bradshaw where they are the quarry and Mr. Burns is their hunter.
I’ve Grown a Costume on Your Face:
It’s the Springfield Semi-Annual Halloween Party but the costume contest goes awry when a real hideous witch turns everyone into real-life versions of their costumes.
Season 18 Episode 4: Treehouse Of Horror XVII
Married to the Blob:
After eating mysterious green goo from a meteorite, Homer grows to massive proportions while he eats everything in sight.
You Gotta Know When to Golem:
Bart takes control of a Golem of Jewish folklore, and forces the ancient statue to do his bidding by writing instructions on scrolls and placing them into the Golem's mouth.
The Day the Earth Looked Stupid:
Taking place in 1938 Springfield, the townspeople react to Orson Welles’ famous War of the Worlds radio broadcast. However, they pay no attention when Kang and Kodos actually do invade the town.
Season 19 Episode 5: Treehouse Of Horror XVIII
E.T. Go Home:
Bart and Lisa help Kodos "phone home," but Kodos uses their assistance to secretly plan something sinister.
Mr. & Mrs. Simpson:
A parody of the 2005 film Mr. and Mrs. Smith, featuring Marge and Homer as the title characters.
Heck House:
Flanders decides to scare Bart, Lisa, and their friends straight after they go too far with their Halloween pranks.
Season 20 Episode 4: Treehouse Of Horror XIX
Opener:
When Homer casts his vote for Senator Obama the sinister electronic voting machine instead tallies a vote for Senator McCain.
Untitled Robot Parody:
Bart buys a possessed Malibu Stacy convertible for Lisa for Christmas. A Transformers parody ensues.
How to Get Ahead in Dead-Vertising:
A group of ad executives discover Homer and his talent of killing celebrities. With the celebrities out of the way, the advertisers can use their likenesses and not have to pay royalties.
It's the Grand Pumpkin, Milhouse:
A parody of It's the Great Pumpkin, Charlie Brown starring Milhouse as Linus, Lisa as Lucy, and Bart as Charlie Brown.
Season 21 Episode 4: Treehouse Of Horror XX
This year’s triple threat of Halloween hilarity sees Moe using Homer’s blood for beer, Bart and Lisa caught in a murder pact, and everyone in Springfield becoming zombies thanks to Krusty Burger’s latest sandwich.