Have Mustadio in Chapter 4. After Bervenia, go to the mining town of Gollund. At the tavern, read the "Rash of Thefts" rumor. Go to the merchant city of Dorter. At the tavern, read the "A Call for Guards" rumor. When you leave the city, a battle will start. Win the battle with Balthier's help, and he will join you.

Have Mustadio in Chapter 4. Go to Goug, and read the rumor at Gollund. Go to Lesalia, and invite Beowulf to Gollund. He will join your group after a series of battles.

Have Mustadio in Chapter 4. Successfully complete all ten levels of Midlight's Deep, and The Byblos will join your group.

Win a match at one of the corresponding venues in Career mode to unlock it:

Madison Square Garden
The Staples Center

Defeat Ko Rey Mo in the light heavy division in Career mode to unlock him.

Win the Burger King event in Career mode. Then at the trainer selection screen, press Down until the Burger King appears as a choice. He gives you Heart when you fight.

Win matches in ESPN Classic Fights mode or Career mode to unlock various new styles, at random:

Collect the indicated number of parts and combine them to unlock the corresponding weapon:

Heat Seeking Warheads: Collect 700 Parts
Hyper Plasma Ball 1: Collect 300 Parts
Hyper Plasma Ball 2: Collect 400 Parts
Plasma Artillery 1: Collect 200 Parts
Plasma Artillery 2: Collect 300 Parts
Plasma Ball 1: Collect 100 Parts
Plasma Ball 2: Collect 200 Parts
Rocket Launcher 1: Collect 500 Parts
Rocket Launcher 2: Collect 700 Parts
Shock Wave 1: Collect 400 Parts
Shock Wave 2: Collect 500 Parts
Spread Shot 2: Collect 100 Parts

Successfully complete the indicated task to unlock the corresponding option in the "Extra" menu:

Art Gallery: Successfully complete the game. This option allows all unlocked game art to be viewed.

Bestiary: Successfully complete the game. This option displays information about each type of monster you have defeated.

Music Player: Successfully complete the game. This option allows all songs from the game to be replayed.

Time Chamber: Successfully complete the Labyrinth Of Time. This options allows you to replay any completed Floor from the Labyrinth Of Time.

Successfully complete the indicated task to unlock more entries in the Art Gallery menu:

While facing one or two other players, do an over the head beat. Before you catch the ball, pass it to a nearby teammate. In the middle of the pass, hold Square to usually confuse the goalie and score. If you do not have any nearby teammates, just hold Square when the ball is in the air to shoot.

Go to the "Game Modes" screen, then choose your team. Go to "Head Start" and set it as desired. For example, if you want to win by five goals then choose "Head Start 4+" so that you will only have to score one goal to win.

Successfully complete the indicated task to unlock the corresponding character: