Mostly; was this a local costume, if not was it tied to the local shop? If the answer is no to those questions, do you still possess the costume, if so would there be any traces of magic attached to it?
Are these sort of things growing worse, or simply larger in scale? Is there a way to trace that? Is it a thing that needs to be maintained, or is it something already done and can only be stopped by ending it?
All questions, if they have an answer that might lead closer to the person or persons responsible.