Easily the most disruptive change to Call of Duty multiplayer is Black Ops 2's revamped Create-A-Class mode. In previous games, players defined custom classes by choosing one primary weapon, one secondary weapon, grenades, equipment, and three skill-enhancing perks. Custom classes in Black Ops 2 now follow a "Pick 10" system, giving players access to ten customization slots to fill with class options and, as a result, far more freedom and variety.

Here's an example: If you find yourself rarely using your secondary weapon, you can simply drop it from your custom class. That frees up a slot for something else; an extra attachment for your primary weapon, perhaps, or a second explosive grenade. Or you could equip a back-up tactical grenade, like the new Shock Charge, which stuns enemies with a bolt of electricity. You can even bend the rules by customizing your class with a fourth or fifth perk. Call of Duty: Black Ops 2's debut multiplayer trailer shows an extreme example, a custom class armed with nothing but a combat knife, revolver, and six perks.

These rule-breaking custom choices are made possible thanks to the inclusion of Wildcards. Equipping a Wildcard will consume one of your ten available slots, but it allows for customization unseen in previous Call of Duty games. With Wildcards, players can equip two primary weapons (rifles, shotguns, SMGs) or affix three attachments (red dot sight, extended clip, stabilizer) onto a single gun.

"It was important for us to challenge our assumptions about Create-A-Class," said David Vonderhaar, game design director at Treyarch. "When we started development on Black Ops 2, we were really passionate about and inspired by the need to challenge all of the core assumptions about what cows were sacred inside the game. So every gameplay system has been re-examined very critically and carefully to be sure that we give the player the utmost control over his experience. All these changes push the boundaries of what fans expect, but we do it in all the right ways that they'll be okay with.

"We didn’t want to take anything for granted. We asked ourselves some very key questions: Why is all content in Create-A-Class so rigidly structured? Do we do this for game balance? Was it usability? Why do we do things that way? What if everything was in a giant bucket?"

Treyarch tested "Pick 10" customization and Wildcards by playing a separate game altogether. Vonderhaar says the studio built a custom, deck-based board game based on Black Ops 2's Create-A-Class system to explore the "core philosophy design at a paper level."

"It allowed us to try ideas, play them out, and test them without writing a single line of code," he says. "I will never design games again without this process."

The process of actually editing your custom classes is quicker and more efficient in Black Ops 2, thanks to the reworked menu system dubbed "the Grid." Gone is the old way of diving into a menu, burrowing deeper, then backing out to the top. Players can now browse weapons, attachments, and perks with a visual carousel a la Cover Flow, making it easier to compare and contrast class options.