Royal MVP Genki Team

At the Team Selection screen in Arcade Mode, highlight Yugoslavia, USA, Korea, and Italy, pressing Start after each. Then, highlight the new team that appears in the top corner, hold Start and press A + B + X + Y.

F.C. Sega team

To unlock the F.C. Sega team, go into arcade mode and press start on the following teams: France, Chile, South Africa, England, Germany, and Argentina. The F.C. Sega icon will appear above the second column of teams. Select it, and then beat the arcade mode (you can continue as many times as needed). Now F.C. Sega will be permanently available in the non-arcade modes under a new menu called "SP".

MVP Royal Genki

To unlock MVP Royal Genki in the SP menu, highlight Yuki Chan, hold down start, and press A. Use the same method to use MVP in arcade mode.

Two new stadiums

In the stadium select screen, before you choose any stadium, hold START and press A. If you do it right you will play in a new stadium.
To get the second stadium just change the stadium in the stadium select screen and do the same trick. When you do the trick for some stadiums you will play in the first stadium and some stadiums will let to you play in the second stadium.

MVP Yuki Chan

To play as mvp yuki chan team (full of funny looking people) highlight yugoslavia but don't press A press start.

AJIM Character Playable

First, defeat AJIM in the normal mode. Then reset the internal Dreamcast clock to April 29th, 2000, and then select the Random character selection with Left Turbo+Right Turbo.