Iggy's Reckin' Balls cheats and cheat codes for Nintendo 64

Cheat menu
Hit R + Z while you are on the opening screen. 
Then, enter any of the following cheat codes:

Code - Results
2ROKTOO - Enable Turok 2 gfx engine     
2TIMES - Enable turbo mode                               
ENTAROADUN - Disable characters except Iggy's girlfriend
GOBABY - Maximum turbos                              
GOOEYGOOGOO - Gooey platforms                          
GOOEYICEPRINCESS - Icy and gooey platforms                  
HAPPYHEADS - Unlock all characters                           
ICEPRINCESS - Ice platforms                            
JUMPAROUND - Stage selection (pause the game play to select any stage)
MICROBALLS - Small balls                       
NONSTOP - Non-stop roller ball                     
OHMY - Random bombs                             
PENCIL - Pencil and ink mode                      
ROLFHARRIS - Monochorme mode                     
SWOPSHOP - Match and Mix mode                       
THEUNIVERSE - Unlock all tracks                               
TOOMUCHFUN - Bouncing balls             
TOOMUCHPIE - Fat balls                        

Unlock extra characters
Win 1st place on each race

Maximum boost
Pressp Jump during on a boost platform.