Faxanadu, being an NES game, didn't really have save slots. You saved your progress with passwords (called "mantras" in game) and they were typically long, convoluted strings of characters. The catch was that if you could figure out which characters signified what you could basically "edit" your "save game" by tampering with a given mantra until you got results. I did that a couple times once I figured out certain things. A number of games had this kind of system on the NES, since the space on the cartridge was rarely enough to allocate space for saves.