I think it's something from Halloween but I'm not sure and I'm not sure of how to remove it. Here's a picture, for reference, since it's not very visible in my actual avatar.

Looks like a zapper skin from Morostide. To get rid of it simply go to the healer and she will remove it from your HA for 25,000sP.

Healer:

http://subeta.net/explore/healer.php

Ohh, thank you very much!!