Dual Wielding. To compensate for the fact that two people are playing, the game pumps up the difficulty for two player. Grabbing both guns and going Guns Akimbo in the Arcade solo and finishing the game? Brilliance.
At the end of the game, while G and Isaac are on their way out via helicopter, they find out that their pilot is a mutant. Without flinching, the two heroes draw their guns and the screen cuts to black. You can most likely guess what happened next.