Hidden Fighters
Complete the game. Characters will be unlocked in this order:
Kuma
Julia
Gun Jack
Mokujin
Anna
Bryan
Heihachi
Ogre
True Ogre

Fight as Doctor Boskonovitch
Select Tekken Force Mode from the main menu. Your first goal is to fight Heihachi's "Tekken Forces" all the way to the Mishima Fortress, where you will hopefully get to fight Heihachi Mishima and defeat him. When you have accomplished this, you will get a copper key. Do this three more times to get the silver and gold keys. The third time you defeat Heihachi, a message saying "Final Stage Challenge" should appear on the screen. You will then go to the Underground stage where you must fight the Doctor. Not only is he very tricky, but the 60 second time limit makes him even harder to beat. Defeat him to unlock him in arcade mode and the Underground stage.

Tekken Ball Mode
Successfully complete the game with ten characters in arcade mode

Fight as Gon
Complete arcade mode using Doctor Boskonovitch. Then, select arcade mode and press the D-pad off either side of the character selection screen. Alternatively, defeat Gon under "Ball mode" or play survival or force mode until prompted for initials, then enter GON

Theatre mode
Unlock each character, including Panda, Tiger, Doctor Boskonovitch, and Gon, and view their endings. The "Disc" and "Sound" options under "Theatre Mode" will now be available.

Record or replay combo
Enter practice mode and choose the "Freestyle" selection. Press L1 + L2 + R1 + R2 + Circle at the freestyle options screen. Then press Down + Select to record or replay a combo.

Alternate introduction sequence
Complete the game with the ten base characters to view an alternate introduction featuring the characters in their two-player mode costumes. For another alternate introduction, complete the game with all characters including the secret characters.

Xiaoyu's School Costume
Play as Xiaoyu 50 times and press start on the character select screen.

Jin's School Costume
Play as Jin 50 times and press start on the character select screen.

Anna's Secret Costume
Play as Anna 25 times and press start on the character select screen.

Gun Jack's Jack Costume
Play as Gun Jack 10 times and press start on the charcter select screen.

High School stage
Unlock Jin or Xiaoyu's extra costume, then get them as challenger in that costume.

Visiting stages
Amusement Park: Get Xiaoyu as challenger in training.
Punk Alley: Get Paul/Bryan as challenger.
Mexican Temple: Get Julia/Heihachi as challenger.
Labrotory Courtyard: Get Nina/Anna/Gun Jack as challenger.
Grassy lands: Get Eddy/Tiger as challenger.
Martial Arts Dojo: Get Forest/Kuma/Panda as challenger.
Taekwondo Dojo - get Hwoarang as challenger.
Skyring: Get King as challenger.
Island Beach: Get Gon as challenger.
Junky Mansion - get Doctor Bostonovitch as challenger.
Forest: Get Yoshimitsu as challenger.
Tiger Dojo: Get Jin as challenger in training/his style clothes.
Chinese Street: Get Lei as challenger.