Big Head Mode
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.
submitted by Jason Dreibelbis (jaybird055@aol.com)

Bonus Heads
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.
submitted by Richard Shelley (peteshelley@compuserve.com)

Bonus Teams
At the "Press Start" 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.
submitted by Julio

Claim Foul Play
When a player is tackled and doesn’t fall, immediately press the d-pad one direction and A, B, L and R simultaneously. (Another way is to press all C buttons).

If done correctly, your player will dramatically throw himself on the flour and claim to be fouled. Beware of performing this maneuver close to a referee, as he will book you.
submitted by Evard Rwelamira

Extra Faces in Player Creation Screen
Complete the International Cup on Level 4 or higher to get clowns faces and aliens faces as choices in create a player.
submitted by Jacob Akcay and Samuel Green

Juggling and Other Tricks
While you are in training, or in a game, press and hold C-Left. 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.
submitted by Cory Fuller

Maradona Spin
While playing, get the ball on offense. Using any player, push the DASH button to perform a dash. During the dash, rotate the control stick 360 degrees to execute a Maradona spin.
submitted by Adam B and Mike A

Overhead Pass
First start running with the stick and the dash button. Release them both and press the left C-button. The player will pass the ball over his own head. This is an excellent way to avoid defenders.
submitted by Benjamin Dover

Play as World Stars
At 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. Be sure to use the d-pad to enter directions.
submitted by Chez

Rotating Heads
At almost any menu which features a player's picture press and hold C-Up then press Z or L to rotate the face to the left, or R to rotate the face to the right.
submitted by Adam B. and Mike A.