The concept of a guy crossdressing and magically turning into a girl has always fascinated me. When I was REALLY young and found TG stories online, there was this one about a guy dressing as a girl on Halloween and waking up the next day still in "costume" where he had completely turned into a girl. His female friend then tells him she will teach him everything he needs to know including how to deal with having a period! Wish I could find it right now. I think it was on the asstr.org archives.
If you crossdressed in public for Halloween this year, be sure to send in your photos!