I can see a Zorua plushie working well with the Pokemon trainer outfit, but that's just my opinion.
As for Halloween Town Xion, maybe the Pumpkinhead or Fatal Crest keyblades would work? They both look sort of Halloween-ish... I also found a picture of some cool boots
on Google, but in general I think some boots with lots of belts/buckles would be kinda neat, lol. And it wouldn't be too hard to attach some little skulls, I don't think.