For the longest time, no colour images existed of Sailor Heavy Metal Papillon, so there was a lot of speculation as to what she really looked like. Thankfully, with the release of the Materials Artbook all questions were answered.
Like all Sailorsoldiers, good or evil, her outfit is based off the standard sailor uniform worn by schoolgirls. Except her get-up is a bit more "lingerie" and a bit less "junior high."
Her creator thought it important to point out that Papillon is sporting quite the manicure, and Papillon's make-up was also described as "thick." I'm going to jump to the conclusion that she's a fair bit older than the good-guys, so her somewhat mature appearance is not surprising. She is a mom after all.
Of course, her main distinguishing feature is the huge wings sprouting from her back - as to be expected from her name. As far as I can tell, they appear to be based on swallowtail butterflies with the distinctive 'tails' at the bottoms of her wings, but not exactly like any one species in particular. Prior to the release of a full-body colour illustration most people were expecting her wings to be rather plain, but Naoko proved us wrong!
So now that you know exactly what she looks like, perhaps you'd like to draw some fanart?
Images from Ladywren's Sailormoon. Horrible translations added to the images done by me.