Fight as Evil Ryu
Successfully complete the game in original mode as Ryu eight times without continuing. Highlight Ryu, then hold Select and press X, Square, or Circle at the character selection screen.

Fight as Kairi
Win all matches in original mode with a Meteo Combo, Meteo Tag Combo, or Character Parade as Hokuto or Nanase.

Skullomania's secret move
Press Low Punch(2), Back, Low Kick, High Punch. Skullomania will do a different Skullo Dream. There is a part with Skullomania and the enemy eating something at a Japanese table.

Fight as True Vega
Get all ten platinum medals in original mode. True Vega will be unlocked in arena mode.

Ryu's secret move
Press Down, Down/Left, Left (quarter-circle going back), PPP and he will dash back.

Hidden characters
Complete original mode with a regular character to unlock one of the hidden characters.
Sagat: Beat the Original Mode game once without continues
Vega: Beat the Original Mode game twice without continues
Garuda: Beat the Original Mode game three times without continues
Shadow Geist: Beat the Original Mode game four times without continues
Kairi: Beat the Original Mode game five times without continues
Pullum: Beat the Original Mode game six times without continues
Area: Beat the Original Mode game seven times without continues
Darun: Beat the Original Mode game eight times without continues
Vulcano: Beat the Original Mode game nine times without continues

Hidden Battles
There are three extra battles available to you in Original Mode, depending on the character you select. Finish every stage with either a Meteo Combo, Meteo Tag Combo, or Character Parade to unlock the respective hidden battle:
vs. Kairi: Hokuto or Nanase
vs. Shadow Geist: Skullomania or Sharon
vs. Evil Ryu: Sagat, Ken, Sakura, and Vega or Vega II

Meteor Tag Teams
Ken/Ryu Down to left, down to the left, triple punch
Sakura/Ryu Low punch,low punch, left, low kick, high punch
Nanase/Hokuto Low punch,low punch, left, low kick, high punch
Pullum/Darun Down to left,down to the left, triple punch
Zangief/Darun 720 degrees, triple kick
Blanka/Dhalsim Left (hold for 2 sec) right, left, right, triple punch
V.Russo/Jack Left (hold for 2 sec) right, left, right, triple punch
Guile/Chun-Li Left (hold for 2 sec) right, left, right, triple punch
Bison/Vega Left (hold for 2 sec) right, left, right, triple kick