Unlock Mini-Game
When turning on the game, tap L and R together repeatedly until the minigame loads up. If you did it correctly, you will see the title screen for the mini-game, Crash Party USA

Geary
Beat him at Teknee

Krunk
Beat him at Terra

Nash
Beat him at Barin

Nitros Oxide
Get at least Gold relics in all the tracks of adventure mode

Norm and Big Norm
Beat them at Fenomena

Velo
Beat the Game