The following are known Game Genie Codes for Mysterium on Nintendo Game Boy.

• 3AD-B38-E6A
  Start with 50% energy
• AF8-78C-E68
  When this is switched on in a battle everyone’s energy is set to max. (This works for the enemy too, so switch off to defeat them.)
• 01D-008-E66
  Start with 1 life
• 05D-008-E66
  Start with 5 lives
• 09D-008-E66
  Start with 9 lives
• FA3-98C-4C1
  Infinite lives