Idk if this is still a thing, but in the pet cemetery, you could see the tombstone of Sparky from Frankenweenie, another Tim Burton movie for those who don't know; they put it there to coincide with the release of the 2012 stop motion version of the movie, which makes sense considering the source material of Haunted Mansion Holiday since Nightmare Before Christmas and the 2012 Frankenweenie movie are both stop motion movies involving Tim Burton and Disney.