Enter these codes on the Matchup screen.
The numbers tell how many times press the TURBO, JUMP and PASS buttons. For example, 5-2-5 means:

Press TURBO 5 times.
Press JUMP 2 times.
Press PASS 5 times. Big Head Team -- 2-0-3 Right
Bullet Passes -- 2-5-0 Left
Fast Passes -- 2-5-0 Left
Fog On -- 0-3-0 Down
Headless Team -- 1-2-3 Right
Hide Name -- 1-0-2 Right
Huge Ball -- 0-5-0 Down
Huge Head -- 0-4-0 Up
Hyper Blitz -- 5-5-5 Up
Invisible -- 4-3-3-up
Invisible Qb -- 3-4-2 Left
Late Hits -- 0-1-0 Up
More Speed -- 4-0-4 Left
Night Game -- 2-2-2 Right
No Cpu Assistance -- 0-1-2 Down
No First Downs -- 2-1-0 Up
No Fumbles -- 4-2-3 Down
No Head -- 3-2-1 Left
No Interceptions -- 3-4-4 Up
No Out Of Bounds -- 2-1-1 Left
No Punting -- 1-5-1 Up
No Random Fumbles -- 4-2-3 Down
Power Blockers -- 3-1-2 Left
Power Defense -- 4-2-1 Up
Powerup Blockers -- 3-1-2 Left
Powerup Defense -- 4-2-1 Up
Powerup Offense -- 3-1-2 Up
Powerup Speed -- 4-0-4 Left
Powerup Teammates -- 2-3-3 Up
Random Players -- 1-1-5 Left
Show Field Goal % -- 0-0-1 Down
Show More Field -- 0-2-1 Right
Smart Cpu -- 3-1-4 Down
Thick Fog -- 0-4-1 Down
Tiny Players -- 3-1-0 Right
Tournament Mode -- 1-1-1 Down
Turn Off Stadium -- 5-0-0 Left
Unlimited Turbo -- 5-1-4 Up

Fat Players:
While playing pause the game and press Up, Up, Left, Left, Right, Right, Down, Down.

True Ending For Season Mode:
To obtain the true ending for season Mode you must beat Season Mode with a rating of 90.0 or higher

Secret Head Codes
After you have chosen arcade there comes up a screen with yes/no pick yes and put:

David-3456
Azpod-4777
Allen-7911
Gatson-1111
Brian-2221
Jove-6644
Bert-8735
Franz-8421
Byron-1969
JUan-6521
Franc-1221
Aubrey-6666