Spark has two reasons that he cross-dresses. One is because he likes to feel pretty, two is because when Mercury and him were in the cell, Mercury always had a dream of trying on different dresses in order to be beautiful, but then the sides of her mouth her slit open and stitch together and now she's self conscious and thinks she's ugly with her mouth, so Spark asks her recommendations on dresses and wears them for her so he can live her dream for her.
