Play as Cammy in Street Fighter Alpha 2 Gold: Finish the game in Arcade mode as M. Bison and get the highest score. Enter the initials CAM at the high-score screen and save the data. Load the saved data, then at the fighter-select screen, put the cursor over M. Bison and press Start twice. Now in Versus mode, you can play as Cammy from X-Men vs. Street Fighter.
Play as Akuma in Super Street Fighter II Turbo: At the fighter-select screen, put the cursor over Ryu, then simultaneously press L1 and R1 to make Akuma appear.