Diddy Kong Racing - Super Boost

Unlock Adventure 2:
Complete everything in Adventure 1. After the second Wizpig race in space and the credits, you'll unlock Adventure 2Adventure 2 Complete Adventure 1

Unlock the Secret Characters
There are 4 hidden characters that can be unlocked:

Taj - Complete Adventure 1
Wizpig - Complete Adventure 2
T.T Beat- all of his ghosts in Single Player Race. It DOESNT include the new unlockable stages
Drumstick - Fling a frog up to the green sillouette shaped frog picture in the world map To the left of Wizpigs face. Stomp on the frog that comes out