Increase your credits up to 5
  When you choose your difficulty setting (the three towers), press UP on the
  control pad. You can increase your credits up to 5.

Keep changing
  On the Kombat Kode screen punch in all fours (push up on all six slots to view
  the number 4.) Doing this will cause your fighter to change every few seconds
  during battle.

Reptile
  When the "Enter Kombat Kode" screen appears before a match, enter the
  following: 192234. (MK, Skull, YingYang, YinYang, 4, Question Mark) If done
  correctly, when you hit START, the screen will say "REPTILE ENABLED". Now, the
  next time you select a character, Reptile will be in the middle where the MK
  design was.

See your character's finishing move
  Do your character's finishing move code after you beat Shinnok without
  a flawless victory you should see your character's finishing move.


Codes
  000 707     25% life (CPU)
  707 000     25% life (Player 1)
  000 033     50% life (CPU)
  033 000     50% life (Player 1)
  321 321     Big heads
  010 010     Disable max damage
  110 110     Disable throws and max damage
  050 050     Explosive Kombat
  555 555     Multiple weapons
  012 012     Noob Saibot mode
  111 111     Random weapon appears in match
  666 666     Silent Kombat
  222 222     Start with random weapon
  002 002     Weapons never dropped
  123 123     Win with one hit
  333 333     Rampler Kombat
  020 020     Block Disable
  192 234     Play as Reptile
  100 100     Throws disabled
  205 205     Fight Reptile
  460 460     Swicharoo
  688 422     Dark Kombat
  987 666     Message1
  123 926     Message2
  985 125     Psycho Kombat


Hints by Felipe Gerhard - felipe.gerhard@gmx.net