It's an open secret that Disneyland (along with many other semi-public places) is a dumping ground for the ashes of people who loved it in life, and, of course, the Haunted Mansion is a frequent recipient of these remains. In a Disneyland Guru post, we are told of a set of ashes that were accompanied by an urn bearing a plaque reading "Rest in Peace our Dearest Grandma Joyce." The Haunted Mansion castmembers supposedly discovered the urn beneath the sod in the Mansion queue's spooky gardens, and installed it with its own shrine in one of the backstage catwalks that run through the upper reaches of the Mansion.
I've done some dungeon-crawling through the bowels and lofts of the Mansion's show-building and have never seen this shrine, but there's a lot of space in that building (and the shrine might have been gone by the time I got my tour).
One of the less discreet families had a dearly departed grandmother Joyce and decided to sprinkle her remains inside the Haunted Mansion. On one of the security cameras (yes, there are many) they saw people throwing plumes of powder from both sides of their Doom Buggy. The crew stopped the ride, but were unable to identify which car was sprinkling the remains.
That night at closing, one of the cast members noticed that some of the plants had been pulled up in the flowerbed near the ride’s entrance. Buried a few inches beneath the dirt was an empty urn with a brass plaque which read “Rest in Peace our Dearest Grandma Joyce,” with a list of family member names engraved beneath.
For several months, the urn stayed in the video camera room inside the Haunted Mansion. But eventually, a few bored employees took the empty urn up into the catwalks inside the Haunted Mansion and made a little memorial for Grandma Joyce somewhere above the graveyard scene. I’m not sure if the urn is still up there, but the odds are that the remains her family scattered throughout the ride are still around.