-To get a dual wieldable version of a handgun, play through a level with only that handgun. You will be able to equip both of the handguns in one weapon slot.

-Collect a weapon that is not in your inventory during the game, then have it equipped when completing the level. When the next level begins, it will be a part of your available inventory.

-Complete all Single Player mode levels with a character to unlock his or her custom weapon. After unlocking it, the weapon can be used by any character.