International Superstar Soccer '98 Cheats (Nintendo 64)

Complete the International Cup on Level 4 or higher. Once you have viewed the end sequence
go to create player. At the "head select" screen press the Left Shoulder button. This will
take you to page 11 and a selection of strangely unusual heads.

While you are in training, or in a game, pree and hold Left-C. The player will start doing
tricks, such as rolling the ball up on his foot and juggling it around on his knee and
feet and head. Different players have different tricks

Big Head Mode
Press C-Down(2), C-Up(2), C-Right,
C-Left, C-Right, C-Left, B, A. Then, hold Z and
press Start as PRESS START flashes on
the screen. 
Zidane's Head
Using the
player creation scren, choose a name and position
for a player. After highlighting any face, hold
C-UP, then hold L or R and Zidane's face
will be seen.
Weird Heads
After beating
the International Cup at #4 diffiulty or higher
you can go to the player creation screen and find
a strange set of heads by pressing L.
Extra Teams 
AS PRESS START
flashes on the screen, press Up, C-Up,
Up, C-Up, Down, C-Down, Down, C-Down, Left,
C-Left, Right, C-Right, Left, C-Left, Right,
C-Right, B, A. then, hold Z and press START.
You will hear a sound if entered correctly. You
now have 5 extra teams. You can also beat the
League Championship at a difficulty of 4 or
higher, then play and defeat the World Stars team
to get the extra teams.
Extra
teams:African Stars, Asian Stars, All American
Stars, Euro Stars A, Euro Stars B 
World Stars Team
As the phrase START flashes on the
title screen Press Left, C-Left, Right, C-Right,
Left, C-Left, Right, C-Right, Down, C-Down, Down,
C-Down, Up, C-Up, Up, C-Up, B, A then HOLD Z and
press START
Forced Foul
When a player gets tackled but does
not fall quickly hold the D-Pad in any direction
and press A + B + L + R OR C-Left +
C-Right + C-Up + C-Down

If you finish the league at any difficulty, and win, you can play
  against the World Stars. When you win the World Series at level 4 and defeat the World
Stars, you'll have access to 5 more hidden teams. The teams are: Euro Stars A, Euro Stars
B, African Stars, Asian Stars, All American Stars.

Complete the International Cup on Level 4 or higher to get clowns faces and aliens faces
as choices in create a player.

When creating a player, at the point disribution, press C-up for
  more abillities for your created player.

Wait for the words "Press Start" to flash on the title screen. Now press C-Up, C-Up,
C-Down, C- Down, C-Left, C-Right, C-Left, C-Right, B, A. Now hold the Z button and press
Start. You'll hear the announcer shout to confirm the code.