Fear makes devils stronger. Guns are highly feared. Generally speaking simply Death Devil could be stronger, but maybe that's too abstract for a devil to be born out of? A Disease Devil could be horrifying, perhaps a more specific one, like Cancer Devil. However, as bad they could be, they wouldn't necessarily kill you immediately like Gun Devil, so they could possibly be destroyed before they caused a horrific amount of damage. It could be funny to see some technically powerful devils based on very concrete and powerful fears, such as Unemployment Devil. What would the fight against it be like, haha. Also kind of abstract, but still easy to imagine would be Hunger Devil. We have already seen it a long time ago in Elder Scrolls... It probably wouldn't appear in any developed country, though.