Alternate floors:

Complete all sixteen practice rounds. The background color will turn
red to confirm correct code entry. Enter the options screen and select
the "Floor" option to choose a new floor pattern and background color. 

Alternate shapes:

Enable the "Alternate floors" code. Complete all modes except practice
and multiplayer and achieve an "OK" rating. The background color will
turn green to confirm correct code entry. Select any game mode other
than practice mode. Select the man that represents the pieces to change
him into a duck. Begin game play with triangle, rectangular, and square-
shaped pieces. 

Control water:

Hold C-Up or C-Down at the main menu to raise or lower a whirlpool of
water. Keep holding either button and press the Analog-stick to move the
whirlpool across the water.