Not just a single modern handgun.

The good guys are all elves and fairies and whatever fairytale creatures, using magic and swords and spears, while the bad guys are all orcs and robots and whatever abominations using tanks and rifles and projecting Nazi propaganda and war imagery TO THE SKY to scare the good guys.

Oh, almost forgot: one of the aliases of the evil twin is just “the führer”, and his throneroom is in the shape of a swastika, with the throne in the middle. The film isn’t too subtle.

The funniest instance I’ve seen of this trope is in the film Wizards (1977, Ralph Bakshi animation) where a fairy queen gives birth to twins, named Avatar and Blackwolf. You can probably guess which one grows up to be the good, kind, hippie gnome, and which one basically turns into a sickly Saruman with skeleton arms.