Every full moon, the Demoman succumbs to a terrible curse. Ghostly armor projects onto him, telling him to take up their cursed blade and use it to kill humans in battle. Fortunately for Demoman, that's basically his job.

Normally, such a helmet would be difficult to wear, and would throw any inkling of peripheral vision out the window. Fortunately, this ghost helm is transparent, and only causes minor cursing when looking through it.
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The TF2 Emporium 2013 Halloween Special is out now, guys! If you want a mod release, you can get it here:

http://halloween2013.tf2mods.net/