Harley Quinn is without a doubt the costume I see most at conventions. There are a ton of iterations of the red, black, and white ensemble between the comic books, video games, and animated series. Morgan, also known as Moaglin, decided to tackle the costume from Batman: Arkham Knight. She pieced the outfit together and customized it. The boots (pictured below) started as straightforward black ones that she painted and added studs to. She managed to get a really nice red considering she started with a black base. She also made the corset and styled and colored the wig.
See some WIP pictures below and even more at Facebook.