Earn the Team: 
Collect the 3 hidden stars on Graveyard GP. 

Hovercar: 
Win the Platinum Cup in challenge mode. 

Bird's Eye: 
Collect the 3 hidden stars on Perilous Places GP. 

Color Tint: 
Collect the 3 hidden stars on Hoedown GP. 

Concept Art: 
Collect the 3 hidden stars on Jungle Jamboree GP. 

Micro Marble: 
Collect the 3 hidden stars on 911: Emergency GP. 

Micro Soccer: 
Collect the 3 hidden stars on Beachside GP.