So, I am a huge fan of costumes and any excuse to dress up is a good excuse.
I know Disney doesn't like adults to dress up in costumes as it can confuse guests as to who is the real face character and who is just a guest in a costume, but I can't find any information about costumes in Movie World.
Do they prevent entry if you are dressed in a costume?
I was planning on a costume I have never seen at MW and I'm not sure if it makes a difference or not, but I obviously don't think its a good idea to impersonate one of their main face characters like Batman or Catwoman.