You must first complete all mission objectives in the single player game before the cheats become available. Then, during gameplay, press BACK, then press the following buttons to activate the corresponding cheat:

• God Mode (Player): X, X, A, B, A
  
• Big Heads: A, X, B, Y, A
  
• Big Bodies: B, B, Y, X, X, A
  
• Chicken Explosives: X, X, Y, A, B
  
• Paper Mode: B, A, X, Y, A
  
• Slow Mo: Y, Y, B, X, A
  
• Fast Run: A, A, X, B, Y
  
• High Pitched Voices: X, A, Y, B, X
  

Unlock Characters:

• W. Jacobs - Complete Special Objective in Campaign Mission 1 on any difficulty
  
• H. Ramirez - Complete Special Objective in Campaign Mission 2 on any difficulty
  
• K. Henkel - Complete Special Objective in Campaign Mission 3 on any difficulty
  
• J. Stone - Complete Special Objective in Campaign Mission 4 on any difficulty
  
• S. Grey - Complete Special Objective in Campaign Mission 5 on any difficulty
  
• B. Gordon - Complete Special Objective in Campaign Mission 6 on any difficulty
  
• A. Galinsky - Complete Special Objective in Campaign Mission 1 on Recruit during a Quick Mission in Mission Mode
  
• D. Munz - Complete Special Objective in Campaign Mission 2 on Veteran during a Quick Mission in Mission Mode
  
• N. Tunny - Complete Special Objective in Campaign Mission 3 on Elite during a Quick Mission in Mission Mode
  
• L. Cohen - Complete Special Objective in Campaign Mission 4 on Recruit during a Quick Mission in Mission Mode
  
• G. Osadze - Complete Special Objective in Campaign Mission 5 on Veteran during a Quick Mission in Mission Mode
  
• S. Ibrahim - Complete Special Objective in Campaign Mission 6 on Elite during a Quick Mission in Mission Mode
  

Unlock Modes:

• Chicken Mode - Complete Campaign Mission 8 in Firefight Mode on Veteran. You must use a full team and none of your teammates may die.
• Slo-Mo Mode - Complete Campaign Mission 5 in Recon Mode on Elite. You may only use one soldier.
• Meganoggin Mode- Complete Campaign Mission 7 in Defend Mode on Recruit. You must use a full team and none of your teammates may die.
• Paper Mode - Complete Campaign Mission 6 in Firefight Mode on Veteran using only one support soldier.
• Helium Mode - Complete Campaign Mission 4 in Defend Mode on Veteran using only one soldier.
• Run Fast Mode - Complete Campaign Mission 1 in Recon Mode on Elite using a full team.