Race Backward:

 To race on  backward  tracks, start a game  in "Arcade Mode." Then, at
 the "Select Game" screen, put the cursor on either  "Championship"  or
 "Practice." Then  hold  Y and press C. When your car appears, you will
 be facing backwards on the track.

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Race as the Hidden Car:

 Press X, Y, X, Y, X at the  mode-select  screen. Then pick Practice or
 Championship mode. At the  car-select  screen, keep pressing Down, and
 you can select a hidden car.