We are HUGE horror fans here, so Xmas includes a couple of darker films for us .. and the 70s classic 'Black Christmas' is one of them!
Someone 'living in your attic' and people disappearing as they are left alone are classic horror tropes. It's a bit dated (and not just the 70s curtains & upolstery) and gruesome but it made the family list, so I had to include it - just don't watch if you're squeamish or alone in the house!