People are always dressing up their dogs. Canine accessories abound in the market and they all look very cute with them. (Or ridiculous, obviously, depending upon the accessory and their owner's taste.)
But why not the cats? Ok, they are independently minded creatures with a great line in disdainful looks. That's no reason not to let them play dress up! Particularly with Halloween causing every other creature in the household to don their costumes!
Your cat will just love a unicorn horn. You know it.