Instead of having effects and silly things added to the gun. The stances like this should instead change the animations of the caster.

The Bard pulls his bow back and summons magical arrows instead of getting them from his quiver before firing. This would be kind of like it does in Madoka Magika!

The Machinist changes the stance to grab his weapon in both hands and fires from his hip for more damage. This would be how a stormtrooper holds his weapon and fires from the hip, making it deal more damage. However since your not a stormtrooper it would be far more accurate!

The Dark Knight changes his idle sword stance to a more offensive one instead of a defensive one. This is already in the game and is used by "Regula van Hydrus". It works really well and looks really cool. He holds his sword up in-front of him.