Absolutely LOVE the wall decal in place of the headboard — bonus: it comes in different colors, which is great to play off the color of your wall. (source: www.dalidecals.com)
One of my favorite types of wall decals is the headboard decal. I actually have a bookcase headboard for my bed so I don't need one of these but if I didn't then I'd definitely create the illusion of a headboard with a pretty wall decal.
Lots of companies make stencils that are easy to apply and remove anytime. This isn't necessarily a Halloween stencil, but the color scheme feels perfect for the holiday.