While MM2's password system seems pretty straightforward, I've always been fascinated with how other games managed to track state with a 10-24 letter password. Metroid, for example...IIRC, didn't the game also keep track of your current health, besides the progress you made in the game? I guess that state could be encapsulated in just a few of those letters. And the state of progress would be pretty easy to do (A = Kraid beaten, B = Ridley beaten, and so forth) as each individual "scene" resetted its state as soon as you left it.