Codes

Play As Akuma
Go into Versus mode. At the character selection screen, press A + B + C + L + R + P simultaneously. Hold down these buttons down until your opponent has selected their character.
Play as Akuma II
Choose any game speed, and at the character select screen, highlight Ryu for three seconds, T.Hawk for three seconds, Guile for three seconds, Cammy for three seconds, Ryu for three seconds, then press the X button and all three Punch buttons (be sure to press the X button just before the three punch button).If your timing is right, you'll see a silhouette appear, and you'll be playing as Akuma.

Secrets

Start a one player game and get to Bison without using any continues. Akuma will come out to fight you.