Change voices:
Go into the Options screen (where there are 5 items in the menu, starting with Controls), and press 'Select' 40 times. A bell will sound, and the game's voice will change.

Special Boards:
Each track has its own special board - To get these boards you have to beat the 1st Official Time and 1st Trick Points on each course.

Extra Course:
Beat the 1st Trick Points on all 3 courses.

Special Course:
Beat the 1st Official Time on all 3 courses.

Snowman Boarder:
Beat the 1st Official Time and 1st Trick Points on Extra and Special Courses.

Trick Points Table:
On the expert course get the wolf to howl 6 times by sliding between the trees. Start a new game and at the Loading screen hold down L1 or L2 for a Trick Point Table. Press L1 or L2 to turn the table off.

Replay Mode:
Beat the 1st Official Time and 1st Trick Points on all courses including the Special and Extra courses. Start a new game and on the Loading screen hold down Select. You can now change the camera view during the race by pressing Select.