We've been to two so far, with a third planned for early September. SO doesn't do costumes, and honestly, I'm not big on them either. Our first party, I wore a "welcome foolish mortals" t-shirt I got off etsy and some Haunted Mansion Minnie Ears. The second party, we both wore MNSSHP shirts we had bought from the first party the year before. This year we'll be in some kind of basic Disney t-shirts again. You are welcome to wear a costume if you want, but certainly not required and you won't stand out if you are not in a costume.