Codes:

 Level 1  DBDBBABA
 Level 2  ADDCAADC
 Level 3  ACBABBCC
 Level 4  ADDDCACC
 Level 5  DDBDBBCA
 Level 6  CCDBCCDA
 Level 7  AADBDDAC
 Level 8  CADDCBCC
 Level 9  ADAABADB
 Level 10 BADDBBBC
 Level 11 ABBDADDA
 Level 12 DCADCAAC

Cheats:

 Type this during gameplay and press [Enter] to confirm:

 GMPETE - gives you all the powerups
 GMNORM - turns you back to normal
 GMBIGH - gives you a really big head
 GMBORG - turns you into a cyborg
 GMKILL - enemies are easier to kill
 GMGODM - invincibility mode