When you get to him, hes really hard if you don't know what to do. Main problem with him, is hell possess one of your party members (the four you have out). And he/she will attack, also using the summons you have up. And when you kill the party member he/she wont become unpossessed, theyll be fainted, so you can't use them. AND the devil will possess someone else after, so it's not a one time thing. So. To defeat him (because youll most likely die the normal way) is to put all of your djinn on standby, then attack him with your strongest summons. (also I had Daedalus, so that helped me). You might lose one or two of your party, but youll defeat him this way. Course you might defeat him normally, but this way is better.
When you find something you can forge, and bring it to the woman. Save before you give the item to her. Then when you leave, come back, talk to her, and she gives you whatever it is, if you don't like it, or already have it you can restart the game and try again. I usually go for weapons so this helps me alot, but if you don't care what you get you can use this for if you got the same thing as before.
Also you have to save BEFORE you give it to her, if you save after you give it to her, itll have w/e she makes locked in already.
Dont use these. Theres no point to them. Specially the bombs. Youll have djinn that doe the same thing and even if it doesnt take affect at least youll do some damage. Then the claws, and powders and seeds, yeah they do damage with out using PP, but the damage is so low it's stupid. Best thing to do is sell all of them. One doesnt give you much money, but you find so many during gameplay, itll give you alot in total.
All you have to do to defeat the three of them, is attack the chaos hound. You don't have to touch blados and chalis at all. Then when you defeat the chaos hound, the battle will end and youll go into the next part.
Like the ancient devil, use summons. The great thing about star is that he has those ball things. When you use the summons make the most damage go on star and the rest on th balls. The balls will faint, and star being the idiot he is, will take the turn to revive them, giving you extra time to attack, without receiving any damage. I beat him in two turns. Totally awesome.
Dijnn often affect the types of Psynergy you can have. For example Having all your Djinn on standby except a water Dijnn will give you the Psynergy Revive which really comes in handy. So don't be afraid to mess around with what Dijnn you have with you.