To unlock the following characters, in Arcade mode, intentionally lose your first match. When the timer reaches zero, a screen will appear where you can enter codes. Enter the corresponding codes within 10 seconds.
CHARACTER - CODE Classic Sub-Zero - Press Y(8), A, RB(8), B(3), X(5) on controller one, then Y(8), A, RB(8), B(3), X(5) on controller two. Ermac - Press Y, A(2), RB(3), B(4), X(4) on controller one, then Y(4), A(4), RB(3), B(2), X on controller two. Milena - Press Y(2), A(2), RB(2), B(6), X(4) on controller one, then Y(2), A(2), RB(2), B(6), X(4) on controller two.
Note: To save the hidden characters, go to the character selection screen. Pause and exit the game. When you start the game again, enter Arcade mode to load the unlocked characters. Wait until the character selection appears and then exit. You will be able to play with these characters online.