Hi!
A good hint is to write down what combinations you use. For instance, in the Serpent's Castle it took me no more than 15 coins to figure out all combinations to all six doors.
Another seemingly random puzzle would be the elevator maze to get to the serpent queen. Again I mapped the area and where the different elevators took me. I guess mapping is an old trick of the trade for all adventurers. I don't know how I would have got through the eye of the beholder games without it
/Jazzid