Easy hits
After the ball is pitched, press [Space] to pause game play. You will be able to see where the ball is located. Move the pointer to where the ball is, press [Space] again to resume the game, then hit the ball

Pablo speaks English
Go to a screen where Pablo says things. Hold [Ctrl] + [Alt] + [Shift] and click on him. He will now speak in English.

Alternately, hold [Shift] at the screen where Pablo speaks

Big City Stadium and Super Colossal Dome
Win the Backyard World Series in season mode to unlock the Big City Stadium and Super Colossal Dome

Mr. Clanky
Win the Backyard World Series to unlock Mr. Clanky in the trophy box in the clubhouse. Click on him to use him in exhibition mode