Mirror Mode:
Highlight "new" on the Competition screen and press R1 + X and you will get Mirror Mode.

Freestyle Board:
In order to get the freestyle board, you need to place in the top three in the regular competition, which gives you all the courses, then rank 1st in trick points.

Alpine Special Board:
Get a record for time on all the courses. To get the "All Around Special" Board you would need to get the top scores in the Total category for all the courses. These boards rule!

Extra courses:
Rank in the top three in the snowboard competition. You will also receive three extra boards.

Extra characters:

Gray the Alien: Score higher than 38 points on the halfpipe

Snowman: Get all three trophies for all the levels.

Boss: Place first in Mirror Mode

Note: Another way to get Gray the Alien is to get 96 or higher in the big air master.

Alternate Clothing:
At the first screen where it says "Competition, Freestyle, etc" highlight competition and press Down, R1, Up, R1, Down, R2, Up, R2, Up, Up, R1, Down, Down, R2. Then go into free style. Irin will now have a schoolgirl outfit, and Cindy...hehehe.