Thanks to the recent video from RWBY finally explaining a little bit about what Dust actually is, I thought I'd try making a dust weapon along the lines of Weiss' rapier and such. However, a simple magical focus isn't enough for me, so I also made it a flamethrower.
Rifle/Flamethrower/I Don't actually know what to call this thing... mode: The basic idea is that it has 4 large dust canisters that each contain one of the basic forms of dust; air, water, earth, and fire. The User can switch between the different types of dust to achieve different effects by activating different canisters to feed into the gun. It is also possible to combine 2 kinds of dust to achieve more varied effects; but the quick, improvised nature of the combination is less reliable and uses up dust faster than normal. A summary of how the rifle performs with each of the basic modes of dust:
-Fire: Uses a continuous stream of dust to generate a large cone of flame. Good for area attacks.
-Earth: Uses small amounts of dust to fire shots akin to more standard bullets. However larger amounts of dust can be use to fire larger, more powerful rounds. Essentially
-Water (Ice): The rifle emits a supercooled mist that freezes into ice shortly after leaving the barrel. This can freeze areas of the ground, creating difficult terrain, or create rudimentary barriers for defense.
-Air: Fire a blast of air that's good for knocking back foes. It can also be used to propel the user in the opposite direction, allowing for enhanced mobility.
Mixing dust grants access to more elements, like a lightning blast that can combo well with the water element. I won't bother listing all the possible combos since how dust combines hasn't been revealed in detail in the show.
Staff Mode: The spell-casting mode for the user. I won't go into much detail as to what spells can be cast since I don't actually have a character with a semblance lined up for this thing, but the general idea is that he can wield the staff to cast spells based on classical elemental magic. Fire spells for damage, Earth spells for battlefield control, etc. It'd probably be a lot like bending logic in Avatar. There is also a blade affixed to the top in case the user needs to defend themselves in melee and doesn't have time to cast a spell.
While each mode uses dust at varying rates, generally it's still very efficient since even small amounts of dust can have drastic effects when used correctly, and due to the size of the dust canisters it's rare that they need to be reloaded even between battles unless the fight was particularly straining or long. It's common to not have to reload for days or weeks at a time.
Generally speaking, the reason for each mode is that one is based on the user's aura and semblance, while the other is purely mechanical. So for instance using the staff takes more skill and concentration, while using the rifle takes no additional effort beyond normal weapon use. The rifle form is also generally more controlled and consistent, at least when not mixing dust. The Rifle form is limited to only 1 specific use for each kind of dust, but can combine colors for additional effects, while the staff form allows the user to channel more varied spells with each color, but is limited to the most basic elements.
(Oh, the gauge at one end of the rifle shows the type of dust, or combination of dust that is currently loaded. In this case Earth since its canister is on the other side of the weapon)