Play Arcade mode with any character on any difficulty setting. Intentionally 
lose your first match and allow the timer to count all the way down. When the 
timer reaches zero a screen will appear where you can enter codes. Each block 
corresponds to a specific button. You must enter the following codes within ten 
seconds to unlock the corresponding character:

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.