You must first Finish 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:
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
High Pitched Voices:X,A,Y,B,X
W. Jacobs - Finish Special Objective in Campaign Mission 1 on any difficulty
H. Ramirez - Finish Special Objective in Campaign Mission 2 on any difficulty
K. Henkel - Finish Special Objective in Campaign Mission 3 on any difficulty
J. Stone - Finish Special Objective in Campaign Mission 4 on any difficulty
S. Grey - Finish Special Objective in Campaign Mission 5 on any difficulty
B. Gordon - Finish Special Objective in Campaign Mission 6 on any difficulty
A. Galinsky - Finish Special Objective in Campaign Mission 1 on Recruit during
a Quick Mission in Mission ModeD. Munz - Finish Special Objective in Campaign Mission 2 on Veteran during a Quick Mission in Mission Mode
N. Tunny - Finish Special Objective in Campaign Mission 3 on Elite during a Quick Mission in Mission Mode
L. Cohen - Finish Special Objective in Campaign Mission 4 on Recruit during a Quick Mission in Mission Mode
G. Osadze - Finish Special Objective in Campaign Mission 5 on Veteran during a Quick Mission in Mission Mode
S. Ibrahim - Finish Special Objective in Campaign Mission 6 on Elite during a Quick Mission in Mission Mode
Run Fast Mode : Finish Campaign Mission 1 using Recon Mode on Elite using a full team.
Helium Mode : Finish Campaign Mission 4 using Defend Mode on Veteran using only one soldier.
Slo-Mo Mode : Finish Campaign Mission 5 using Recon Mode on Elite. You may only use one soldier.
Paper Mode : Finish Campaign Mission 6 using Firefight Mode on Veteran using only one support soldier.
Meganoggin Mode: Finish Campaign Mission 7 using Defend Mode on Recruit. You must use a full team and none of your teammates may die.
Chicken Mode : Finish Campaign Mission 8 using Firefight Mode on Veteran. You can not let any teammates die and you have to use the full team.
x2ABA 2 means twice-in order to do this code go to the cheat screen
Submitted by The Ruler Of XBOX