To make your team invinicible, press the Analog stick Left+D-pad Down+A while playing the game.

To make just yourself invincible, press the Analog stick Up+D-pad Down+A while playing the game.

To play the No Brain mode press:

Up analog stick + Down D pad then Y

During gameplay

Press:

Up Analog stick down D pad then B

To play with Big Heads press:

Up on the Analog stick + d pad down then press X

During gameplay, hold analog joystick LEFT + D-pad DOWN + B.