The following are known Game Genie Codes for Battletoads / Double Dragon on SEGA Genesis.

• Once Invincible, Stay Invincible for the Rest of Stage
  AWSA-CA3Y
  Note: There are times where you will have to turn this off to advance.
• Your Character Is Invincible And Always Blinks
  RGRA-C610
  Note: There are times where you will have to turn this off to advance. This code may take a while to wear off after you have turned the Game Genie off.
• Your Character Is Invincible
  CCRA-CA9W
  CGRT-CAAG
  Note: There are times where you will have to turn this off to advance.
• You And Enemy Are Untouchable
  KA1A-EA86
  Note: There are times where you will have to turn this off to advance.
• You’re Untouchable While You Have At Least 1 Life
  MT1A-EAG4
  Note: This does not work on Stage 4. This also does not protect you from bullets, electricity, etc…
• Invincible To Bullets, Darts, Giant Hands
  NM8T-CA4Y
  Note: This does not work on Stage 4.
• Invincible To Dynamite While You Have At Least 1 Life
  MTET-EAAT
• Invincible To Electricity
  EJXA-EA56
• Invincible To Stones (Space Stage)
  ADST-CA6R
• Invincible To Bullets (Space Stage)
  ADKA-CA7Y
• If You Hit An Enemy You Will Get An Extra Life
  BAWT-EA2C
  Note: You cannot have more than 127 Lives.
• Autofire On Stage 4
  RGMA-C612