To play as Akuma, on player one's side, at the character select screen, highlight Ryu and hold the start button. You must continue to hold the rest of the sequence. Move the cursor down, left, down, left, down , left, down, left. And continue to hold the joystick left at this last step. While holding start and left press an action button. Then, Akuma will be your selected character.
On the character select screen, highlight Morrigan (highlight Felicia if your Player 2). Press and hold the Start button. Press Down 13 times on the joystick and press any button.