Instructions
Open the options menu and set the game to the easiest difficulty. Set each match as one round and give yourself unlimited time. Exit the option menu and begin a new game on Arcade Mode.
Unlock the six console-exclusive characters first by beating Arcade Mode with certain characters. Beat the game as Ryu to unlock Sakura, C.Viper to unlock Cammy, Sakura to unlock Dan, Abel to unlock Fei Long, Chun-Li to unlock Gen and M.Bison to unlock Rose. You have the option to unlock Akuma once you have unlocked these six characters.
Beat Arcade Mode again with at least one perfect round to unlock your chance to fight Akuma. Defeat Akuma in combat using your best moves to unlock him as a playable character. You cannot use any continues when playing Arcade Mode for Akuma.
Complete Arcade Mode using Akuma to unlock the option to unlock Gouken. Play Arcade Mode again using a character you have already beaten the game with once you have completed the game with Akuma and unlocked his ending movie. You must get at least one perfect round and you cannot use any continues. You will face Gouken at the end of the game. Defeat him using your best strategy to unlock him.
Complete Arcade Mode with every single character in the game, including Gouken. Seth will then become available as a playable character in all game modes.