Tekken 3

Fight as Kuma:
Complete arcade mode once.

Fight as Juila:
Complete arcade mode with two characters.

Fight as Gun Jack:
Complete arcade mode with three characters.

Fight as Mokujin:
Complete arcade mode with four characters.

Fight as Anna:
Complete arcade mode with five characters.

Fight as Bryan:
Complete arcade mode with six characters.

Fight as Heihachi:
Complete arcade mode with seven characters.

Fight as Ogre:
Complete arcade mode with eight characters.

Fight as True Ogre:
Complete arcade mode with nine characters.

Fight as Panda:
Highlight Kuma at the character selection screen and press Circle.

Fight as Tiger:
Successfully complete the game with eighteen characters. Then, highlight Eddy at the character selection screen and press Triangle.

Fight as Doctor Boskonovitch:
Complete Tekken Force Mode four times (collect the bronze, silver, gold keys, then complete that mode one final time). Defeat Doctor Boskonovitch when he appears to have him available on the character selection screen under 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

Beach Ball mini-game:
View All endings of the ten base characters to enable the "Ball Mode" option.

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.

Alternate costumes:
Select arcade mode, highlight a fighter on the character selection screen, and hold R1 + R2 + L1 + L2 until the timer reaches zero. Release the buttons when both fighters are displayed.

Alternatively, play as the desired character the indicated number of times. Then, highlight that fighter on the character selection screen and press Start: Ling Xiaoyu (fifty times), Jin Kazama (fifty times), Anna Williams (twenty-five), Gunjack (ten).

Infinite combo:
Enter practice mode and select King. Select combo practice and choose combo 1. All you have to do is that combo, but with only I Ali Kick (the sweep-like kick near the end). Then execute the combo repeatedly, with only one Ali Kick at a time. The game will go to a 99 Hit Count, before the counter resets and starts over.