Here is a video that talks about the Nightmare Before Christmas overlay that they do at The Haunted Mansion in Disneyland.
Halloween and Christmas are a great time to go to Disneyland, but be warned, the crowds are HUGE at Christmas time. If you want to see this aspect of the Haunted Mansion, GO NOW! It’s so much better than when the park is packed with people at Christmas.
Here is another video describing a new feature of the WDW Haunted Mansion and their hitchhiking ghosts.
I want to see this so bad that I think we’ll be driving for four days straight just to get to the other side of the country and go to Disney World.