About half the adults wear costumes and many more wear Halloween themed shirts. Some of the guests looked very much like Disney characters, but as long as you don't sign autographs or encourage other guests to pose with you, you'll be fine. One thing to keep in mind is it is still hot and humid in September so think cool when planning your costume. These are the guidelines that were posted in last year's MNSSHP Guest List and Discussion thread on the disboards. There will probably be a new thread started once this year's party dates are announced:
Costume rules for MNSSHP:
Halloween costumes should not:
--Obstruct the guest's view or interfere with their ability to board/unload from attractions and/or the Walt Disney World Resort transportation system (including monorails, ferry boats and motorcoaches)
--Drag on the ground
--Contain sharp or pointed objects or material that may accidentally strike another guest
--Be offensive to other guests
--Contain any weapons which resemble or could be easily mistaken for an actual weapon