Alternate costumes:-  Highlight a racer and press Z at the character selection screen.

Quick start:-  Press A immediately before "Go" is announced and the light turns green.

Try mode:-  Successfully complete training mode under the beginner and master difficulty settings to unlock the "Try" option on the training menu. 

First Place: Unlock All Time Trail Weather Conditions for Expert Difficulty.

Second Place: Unlock All Time Trail Weather Conditions for Hard Difficulty.

Third Place: Unlock All Time Trail Weather Conditions for Normal Difficulty.

Unlock Hidden Tournament Password Option At the Options Menu, press the following at the same time:-  X + Z + Start

This will open up a Password option. To compete in official Time Attack Challenges, enter passwords here. 
 
Unlock Secret Tracks Complete Championship Mode on the following settings to unlock the corresponding tracks:

Cool Ocean: Beat Championship Mode on Normal setting.

Aqua Maze: Beat Championship Mode on Hard setting.

Victory Gate: Beat Championship Mode on Expert setting. 

Weather:-  Successfully complete the Expert Championship in first, second, or third place to respectively unlock the weather conditions in Time Trial mode under the expert, hard, or normal difficulties. 

Victory Gate track:-  Successfully complete the game in championship mode under the expert difficulty setting.

Cool Ocean track:-  Successfully complete the game in championship mode under the normal difficulty setting.

Control title screen:-  Press the Left Analog-stick when "Start" appears on the title screen to move it on the water.

Control loading screen:-  Press the Left Analog-stick while a track loads to control the water.