BARGAINBASEMENT Have all vehicle abilites  

WACKYSPOILERS   Have all cars  

WACKYGIVEAWAY   Access to all tracks

CRACKEDNAILS    Extra Hard Mode 

Hints

Get the Mean Machine:

Win the champion races with any character.

Get the Dude in the Airplane:

Complete the single races with any character.

GameShark Codes

Always Have 10 Muttleys      
8E938D7E000003FF
 
P1 Inf Tokens - Battle Arena 
D27881090000000A  

Infinite Retries - Wacky Cup 
F02DD61700000005
 

Thanks to Revolution readers Prototype 35, GZA and Vince Lombardi!