International Super Soccer 64
Big Headed Players
To get "big headed" players in International Superstar Soccer 64, just enter the following code at the title screen: Top C, Top C, Bottom C, Bottom C, Left C, Right C, Left C, Right C, B, A, and then hold down Z and press Start. Look familiar? Yep, it's the old Konami code. Anyway, if you did the code correctly, the announcer will say "Goal!" Then once you actually start the game (but not before), the players will all have big heads.

 Big Headed Players
 Hidden Items
 Infiltrate the Score

Hidden Teams
International Superstar Soccer 64 contains six additional, hidden teams. To get these extra teams,all you have to do is enter the code below (use the Control Pad for the directional input):
Up, L, Up, L, Down, L, Down, L, Left, R, Right, R, Left, R, Right, R, B, A, and then hold down Z and press start.
If you did the code correctly, you'll hear the announcer say, "What an incredible comeback!" Then go to the Team Selection screen, and you'll see a seventh group of teams -- All Stars. This group includes Euro Stars A, Euro Stars B, Asian Stars, African Stars, All American Stars and World Stars.
NOTE: In the Japanese version of this game, J-League Perfect Striker, the aforementioned code only gives you two new teams.

Infiltrate the Score Rankings
First, you should start a league and, after you've played a game, save it. Next, when you can see the "score rankings," remember those players and press reset. Then go to the trade screen under the Option Mode and trade those players with anyone you want. Now press reset (not on the machine but in the menus) and cancel that trade. Then go to the saved league and check the score rankings. They should be changed.