To access these modes enter the combinations at the title menu, be aware that achievements will be locked if you do so.

Effect	Code
Player 1 God Mode	Up, A, X, B, Y, Down.
Player 2 God Mode	Down B, X, A, Y, Up.
Slice Mode for Single Player	LT X A X A RT.
Sudden Death	X, RB, Up, Down, LB, A.
Zombie Mode for Single Player	Y A A A X B.