We should have to collect items via drops (like Jade Wind Orbs) and quests and trade these items for a mask of our choice. People who collect loads of 'orbs' can get all the masks

Would add a greater variety of costumes in towns too, would hopefully be easier to code as the mask templates exist already and give us mask collectors something to crave.
Plus our resident Mad King could still give out his pumpkin-themed head attire.