This pauldron can attach over any standard armor. The pauldron is lovingly crafted of Mithral. There is a mechanism for an actuated arm that can move freely on the shoulder with a large cannon that looks like a mini gun. 

On your action you can spin up the barrels with the command word, and the canon will fire magic missiles at 9th level. 

The canon can be fired twice per long rest, with time taken to recharge the arcane power within the canon. If you attempt to fire the canon more than twice per long rest, the canon will overheat and melt being ruined forever.