Harley Quinn Diy Costume . Used bat sanded it down, then paint and stencils and sharpies. And yes, her signature diamond tattoos. Harley Quinn Arkham Knight DIY Costume / Cosplay + Halloween love from www.lovemaegan.com She is portrayed by margot robbie. Used bat sanded it down, then paint and stencils and sharpies. After breaking the joker out of the arkham asylum she worked in, the two form a relationship that drags her into a life of.