Enter these codes at the cheat screen:

TOMTHUMB    Small Players
BCHBLKTPTY  Big Baseball 
WLDWLDWST   Baseball Trials
MYEYES      Blurred Graphics
FLYAWAY     Back to Dougout
HOLLOWBATS  Aluminum Bats 
WTOTL       Blackout 

Team Lizard:
While at Kaufmann Stadium, choose an exhibition game. When a player hits either sign that reads "Win a lizard", the whole team will become lizards.

Slow Down Pitch:
When pitching, if you want to slow down your pitch a little or a lot, hold down the A button and this will slow down your pitch. The longer you hold A button down the slower the pitch will go.

GameShark Codes

1 Strike And You Are Out  d106a2780000
                          8106a2780002
 
2 Balls And You Walk      d106a2760000
                          8106a2760002
 
2 Outs And You Are Out    d106a27a0000
                          8106a27a0001

2 Strikes And You Are Out d106a2780000
                          8106a2780001

3 Balls And You Walk      d106a2760000
                          8106a2760001
 
Away Team Scores 0        80060d0b0000

Away Team Scores 50       80060d0b0032

   
Home Team Scores 0        800599830000

Home Team Scores 50       800599830032
 
Infinite Balls            8106a2760000

Infinite Strikes          8106a2780000

Infinite Creation Points  8110534042ba
 
Infinite Pitch Type Points81105a544200

1 Ball And You Walk       d106a2760000
                          8106a2760003

1 Out And You Are Out     d106a27a0000
                          8106a27a0002

Big Ball Mode             800296320001
  
Ball Trail Mode           800296360001

Tom Thumb Mode            8002963a0001

   

Thanks to Revolution readers Gary Shimura and Mike Malpass!