From the main menu, go to "Options" and then "Cheats." Type in your desired code and click on the double arrow icon in the bottom right corner to input the code. You can input multiple codes while on the screen, so no need to back out and go back into the menu in input multiple codes.

• BEASTSBEWARE - Unlimited Bullets
  
• CANTTOUCHME - Unlimited Health
  
• CATCHMEIFYOUCAN - Hyper Speed mode (WARNING: You run the risk of going out of bounds using this!)
  
• DINGDING - Invisible Karts mode
  
• HOPPITY - Boost Jump mode (WARNING: You run the risk of going out of bounds using this!)
  
• ICANDOTHISALLDAY - Unlimited Stamina
  
• IMOUTTATIME - Unlocks all non-secret characters
  
• SPLATSILVER - Paintball mode (Doesn't seem to work at the moment)
  
• TOPHEAVY - Big head mode
  
• YEAG - Unlocks Bunlith and makes the announcer say "yeag" (To select Bunlith, move your cursor to Fodder and press down until you see her.)