Gunfire Reborn

Rouge arsonists are the Big, fat and slow enemies that start to use a flamethrower when you get up close. I encountered them the most in the 2 Area that is covered with Sand.
I personally got this without trying but i was using the "justice" gun alot to blow them up.
Justice is the little red lizard gun that shoots lava balls with RT and you have to detonate them with LT.
Overall its a really strong gun in general but not good against enemies that are far away. Without the gun you could just lock them up with the purple LB ability of the standart character and then shoot the tanks they carry on their backs.

The best way to unlock this achievement from a matter of doing this sooner is playing as Crown Prince and freezing the Rouge Arsonists with his energy orb attack using , then use Dash to work to its back to face the barrel and center your reticle at them before firing.