if you get the option to do a gaiden chapter, do it. at around chapter 16 or so you'll get the option to do chapter 16x. this is the port of badon. here, you get the only dark magic user in the game, and my god is he good. his name is canas, and it's definetely worth it to train him. Also, in this game you should really wait until level 20 to promote people(especially canas).