To change the floor set beat all of the 16 practice rounds. Then go to options. There will be a new option allowing you to change the floor setting.
First, beat all the practice rounds. Then get an OK in all the modes of play except for practice and multiplayer. Now in all the modes of play except for practice you will see a little guy. Click on him to change the tile set.
To activate this cheat, you have to get the top score in "Classic" mode and enter your name as "imani".
While on the main menu where you select the mode of gameplay, if you hold C-Up, a tall spike of water rises from the pool. Move the control stick while holding C-Up and the column of water moves across the pool. Holding C-Down results in an inverted spike.