Three characters of mine are participating in the Grand Galloping Gala, so of course they all needed outfits, the third of which was a conceptualization of Dawnguard's formal outfit.
This would have actually been my favorite outfit if I had come up with it by myself. It is, in fact, a variation on Owain's outfit, a character from Fire Emblem: Awakening of whom Dawngaurd is based off of.
I was planning on drawing him in a tux or more traditional formal outfit, but really felt that a modern outfit wouldn't fit Dawnguard's dramatic and theatrical personality. Which is when I turned to the character he's based off of, tried to fit the outfit to a pony's body, and played around with colors.
The end result looks pretty good, if I do say so myself. I've certainly received more compliments about Dawnguard than my other two characters, at least!