John Polidora is an artist at Blizzard. You like Mercy's Halloween skin? He did the concept for that. And loads of others, of course. As a senior concept artist and character designer working on the game, that's literally his job. I just thought I'd mention Mercy because as someone who mains as Mercy it is a very good skin that I in no way have complicated feelings about whatsoever.
You can see of Polidora's work at his personal site and ArtStation page.