I have posted a idea a while back concerning a Halloween overlay to Big Thunder, to a Ghost Train kind of experience.....
So why not the Matterhorn as well? Add a new soundtrack, keeping the old howling wind, but also some eerie kind of low music, or the sound of one of those Swiss alpine horns, isolated, blowing occasionally throughout the mountain and queue...just one, short, deep blast at a time. Inside, some new lighting for the dark cave portions, green likely, or deep blue, and for Harold as well and increase the volume on his growls.
A few simple new props could be added...nothing bloody, but frozen portions of skeletons near the crystal cave/Well's expedition crates, and around Harold in his two appearances...add in some fog effects for the caves, and the new soundtrack, and I think it would be good to go. If they wanted to do a bit more ambitious overlay (unlikely), they could add a projection scene in the current snowflake field on the lift hill, of the outline of Harold glaring at you, eyes lit only, the rest dark, and then running off...say from shoulders up only, as if they screen was a opening into another cavern.
What do you think? Should the Matterhorn join in the Halloween festivities?
And on to the second portion of my idea...why not introduce for the month of October a Ichabod Crane character to Fantasyland, to talk to guests, and at night perhaps have a mini show back by Small World, from the parade gates, and around, with the end/exit area being the closed off Toontown, since it would be after dark. There would be some lighting effects (lightning/thunder), fog, and music, with Ichabod telling the story of Sleepy Hollow, culminating in the appearance of the Headless Horseman doing a ride-by through the fog, and vanishing into the Toontown area via the use of a fog bank (if not dangerous for the horse) and cast members being ready to close the gates behind the performer. True, it would be neccesary to shut down the path for this area, but it would be good to see the characters in the park for Halloween, and this had the most logical setup I could see with wide paths for running the horse and a entry and exit point fairly close to each other.