From what I remember (it has been awhile since I've played), get the gold trophies on all 100cc races (Mushroom, Flower, and Star). Then the Special should open up. Get a Gold on that too. Now do it all on 150cc, and the All Star Cup Tour opens up (all 16 tracks!). When you do that, then the mirror mode opens up (on 150cc of course). Do it all again, and then you should have completely beaten the game with a nice shiny prize at the end!