The Haunted Mansion crew, over the years,
has come to meet many characters originating
from other franchises (be it an official crossover,
or something we came up with).
Here is a non-exclusive list of works
that are in some way considered canon to
our version of the HM universe.
The Nightmare Before Christmas
ORIGIN: This is a canon crossover -- every Christmas season, the Disneyland and Tokyo Haunted Mansions receive a full overlay featuring characters from the film.
THE CROSSOVER: The attempt of Jack Skellington (the much-famed King of Halloween) to take over Christmas, as all who have watched the movie know, didn't go all too well, as this creature of Halloween had a tough time understanding that Chrismas presents aren't, actually, supposed to be scary. Luckily, Jack eventually found just the right audience for his Halloween/Christmas mashup: the silly spooks of the Haunted Mansion. In his Sandy Claws suit, Jack now visits the manor every Christmas.
Disney's Alice in Wonderland
ORIGIN: This is pure fanon, based on the Hatbox Ghost's uncanny resemblance to the Mad Hatter.
THE CROSSOVER: We posit that the Mad Hatter (real name: Reginald Hatter) is actually the Hatbox Ghost's cousin. He sometimes comes over to the Mansion to visit the Hatbox Ghost, although Hattie, who is not mad at all, highly dislikes these visits and finds Reginald incredibly obnoxious.
Atlantis — The Lost Empire
ORIGIN: Non-canon; originally thought up by AskTheGhostHost, a role-play tumblr blog.
THE CROSSOVER: Late in their lifetime, Dorian and Vincent Gracey began to make extensive research about the lost continent of Atlantis. They were inches away from finding the way to the sunken city when a vital clue came missing: another eccentric billionaire, Mr Whitmore, had bought the Shepherd's Journal before the Gracey brothers could get their hands on it.
ORIGIN: In Madame Leota's spellbook, there is an easter egg -- a ghost-summoning incantation that actually originates in the Disney live-action comedy Blackbeard's Ghost. Whether it's just an allusion or really meant to be evidence that they take place in the same universe is left unexplained. This movie and the Haunted Mansion go well together anyway, with witch Aldeta Teach's portrait looking like a Sinister Eleven painting and the general theme being a silly spook who just wants to have fun in spite of his scary background.
THE CROSSOVER: Not much of a crossover; they just share a universe. As mentioned previously, Aldetha Teach used some spells also known to Madame Leota.