I have an idea.. a gun that shoots out shadows. When you use it, you can make a shadow cloud that acts like a smoke grenade, or you can use it to shoot a shadow strand at someone, and using a pre-entered command, it will make the target do what you want. The ultimate stealth weapon.
Or maybe a chemical frost thrower pistol. It uses an acid of some kind, mixed in with a catalyst to cause a chemical reaction. Then it spews out that fluid like a flame thrower, but instead of lighting people on fire, it freezes them like liquid nitrogen and slowly eats at their flesh and bone.