This is the first Halloween episode of the series to be titled onscreen as "Treehouse of Horror". Every prior Halloween episode was titled onscreen as "The Simpsons Halloween Special", even though the official title that appeared in television listings was "Treehouse of Horror".
In the crowd of clones, you can clearly see Peter Griffin from Family Guy (1999), a Homer with glasses and a Homer drawn in the same design as he had appeared on The Tracey Ullman Show (1987).
This, along with "Radioactive Man", "The Simpsons 138th Episode Spectacular", and "Tennis the Mance", is one of the few pre-EABF episodes to be digitally colored. Starting with "The Great Louse Detective", every episode afterwards was digitally colored.
Simpsons regulars and their animal transformations in The Island of Dr. Hibbert: Willie (shaggy dog), Frink (turkey), Marge (panther), Ned (cow), Mrs. Krabappel (hyena), Jasper (goat), Selma (elephant), Patty (lion), Snake (skunk), Krusty (lion), Apu and the octuplets (possums), Lou (cheetah), Eddie (dog), squeaky-voiced teen (donkey), Rev. Lovejoy (coyote), Ralph (peacock), Comic Book Guy (ram), Grampa (rooster), Quimby (panda), Sideshow Mel (lemur), Manjula (antelope), Chalmers (bear), Moleman (turtle), Moe (toad), Cletus (sloth), Otto (camel), The Rich Texan (buffalo), the Wiggums (pigs), Smithers (flamingo), Luigi (guinea pig), Bart (spider), Maggie (anteater), Lisa (owl), Wolfcastle (rabbit), the Captain (alligator), Dr. Nick (squirrel), Judge Snyder (hippo), Mr. Burns (fox), Bumblebee Man (bumblebee!), Disco Stu (shrew), Kent Brockman (rhino), Martin (sheep), Agnes and Seymour (kangaroos), Nelson (wolf) and Homer (walrus).
This is the final Treehouse Of Horror episode to use at least three writers for separate segments. Starting with Treehouse Of Horror XIV, they would usually only have one writer for all segments.