The center spells out "boo" in some orange-painted alphabet letters from Tim Holtz, mounted on accordion-fold medallions.
Here's one of my favorite pennants, because I love this crazy chipboard bat cut-out. I gave it a little detail with a white colored pencil, and slapped some cat eyes on there so he can see in the dark.
Just for fun, here's another view of the mantel. It's starting to look spooky around here!