Halloween is still two months from now but I want to start preparing a scenario to celebrate the date. Coincidentally, we'll be playing on November, 1st which is date of Sahmain so I'm trying to find a good Pendragon scenario with otherworldly elements. The PK are still in Phase 1 (?), and that session we'll be playing in year 489 AD. I have access to all the books and PDFs of the Pendragon line so I'd appreciate if someone could point me to a good scenario that I could adapt - it doesn't have to be long or involved. I will mix the Pagan elements of Sahmain with whatever you suggest.

The Adventure of the Childermas Game from The Great Book of Pendragon Treasures is one of the best RPG ghost stories I've read. Compact, quaint and with a twist. It's strongly tied to Childermas date though.

The "Story of the Castle Wakely" (Tales of Chivalry and Romance page 18) is about a haunted castle. Might take a little adaptation but should be very much in the spirit of what you are looking for.

Another one that might work is the Adventure "Sir Gorboduc The Fiend" (Great Pendragon Campaign, page 107). This has a small tie in to Samhain.

The Uther Phase is bit early for "The Adventure of the Spectre King", but otherwise the scenario is good Halloween material.