I've got a boxed Zelda II for NES that smells like cat piss - box, manual, cartridge - the whole thing. I've cleaned it all inside and out, left baking soda in the box, everything I could think of and it still reeks. There aren't any stains or anything, however. I've also got a boxed SNES that smells pretty similar, again with no stains or marks. With that one, I'm thinking it's the styrofoam that's the source of the odor.