Unlock the following Game Modifiers by completing Campaign mode on the corresponding difficulties:
GAME MODIFIER - HOW TO UNLOCK
Double-Physics (Doubles force of explosions) - Complete Campaign mode on Medium difficulty.
Hollywood Mode (Enemies have big heads) - Complete Campaign mode on Easy difficulty.
Tough Guys (Enemies have more health) - Complete Campaign mode on Hard difficulty.
Private - Complete the game on Easy Difficulty.
Kaboom - Destroy the gas station.
Poll and Dive - Survive the pool attack.
Droppin Bombs - Call in the airstrike to defeat the Command Center.
Seen Your Video - Watch an unlocked video.
Staff Sergeant - Complete the game on Normal Difficulty.
Long Range - Kill 20 enemies with a sniper rifle.
Color Me Impressed - Complete a mission on Normal without dying, failing, restarting, or continuing campaign.
Hummer - Kill 15 enemies on the HMV turret.
Rocketman - Kill 2 aliens with one Rocket.
Sergeant Major - Complete the game on Hard Difficulty.
One Hundo - Unlock all the unlockables.