Unlock Difficulty Settings: When you successfully complete the game on the Normal difficulty setting you will unlock Easy and Hard difficulty settings.
Unlock Akuma: At the 'Character' screen select the 'Game Speed' option and choose the 'Super-T' fighting style. Then highlight the following characters for exactly 5-7 seconds in this order - Ryu, T. Hawk, Guile, Cammy, Ryu. Then immediately press 'Start' followed by three punches.
Fight Akuma in the Final Round: Complete the game without losing a single round and get four 'Perfects'.