Rattler

 is a gun that simultaneously fires a shotgun blast and a beam that has a chance to poison enemies.

Trivia

 * The pickup line, "Snakes on A Gun," is a reference to the film Snakes on a Plane.
 * The Twin Snakes synergy is a reference to the Metal Gear Solid series.
 * The gun's name is likely a reference to the poem "The Rattler," in which a man is confronted by a snake similar in color to the one wrapped around the gun.