In fact, we know so little about him, he doesn't even have a set personality!
That's where you come in. You need to give this guy a personality. Why does Sombra want to take over the Crystal Empire? Maybe his crystal obsession is actually a misunderstood interest in Geology? Or perhaps Rarity is his long lost relative and he just wanted to say hi, but couldn't figure out the words to use?
Drop your idea after the break!