Enter the options menu and go into the passwords screen. Enter the cheats for their corresponding function:

• MANDARIN - "Achilles Head Mode" 
• PUFFER - "Always Sniper" mode 
• TANG - "Bullet Shield" mode 
• TRIGGER - "Invisible Soldiers" mode 
• HOGFISH - "Perfectionist" mode 
• DAMSEL - "Rubber Grenades" mode 
• GARIBALDI - All Replay Items 
• SPINEFOOT - Huge Arms
• SEAHORSE - "Men With Hats"
• TILEFISH - "Silver Bullet Mode"
• GOBY - "Unlimited Ammunition"
• BUTTERFLY - "Unlocks All Missions"