Ikaness Assassin shares the same skeleton as the standard character [from what I can tell]. And the Bebeg just looks like an awesome giant fluffy mob that would make for a great costume.
I'm gonna keep looking around for other mobs that would make for cool costumes.
update
Astaroth Blades would be a nice new katar.
Edited by Feuer, 14 November 2012 - 05:13 PM.