In Street Fighter 2 Alpha Gold press Start once and press any button to select them. Notice they will have no power level bars on the bottom, meaning you can't use super moves.
All original characters can be selected by pressing Start while selecting the character. This can only be used on characters from the original Street Fighter 2.
Put the cursor on Ryu then simultaneously press L1 and R1 to make Akuma appear.
Select Vega in arcade mode and complete the game in first place with a score greater than 50,000. Enter CAM as initials on the high score screen. Select versus mode, highlight M.Bison, and press Start three times.
Highlight Ryu on Street Fighter Alpha 2 Gold and press Start TWICE. Then press any button to select him. He will be able to do Akuma's Teleport and the 3 power bar special move "Raging Demon" aka "INSTANT HELL MURDER" by pressing Low punch, Low punch, Low kick, Forward, Hard punch FAST.
To play as evil Sakura, highlight Sakura and press Start once so evil Sakura can be selectable.
In the selection menu highlight Ryu, hold L1 and press R1. Now you can play as Gouki.