After you've made it through the Mythril Mine the first time, you are able to recruit Yuffie. This is something I really recomend you do now, and not later. It really helps to have her. She's a pretty good fighter and an excellent stealer, and even though there are times you'll regret it, in the long run, you'll probably want her in your party. Go to any forest location in the world, and wander around until you meet up with a young woman called "Mystery Ninja", who will attack you. She's not that hard to beat, and when you do, you'll have the opportunity to talk to her. DON'T do anything that will make a screen come up over the game screen. (Menu, Save Point, Name Screen, etc.) If you do, she'll steal some of your cash and bolt, forcing you to repeat the whole process over again. Just walk up to her, and when she asks for a rematch, tell her no. She'll then ask if you're scared of her, so humor her and say "...petrified." When she threatens to leave, tell her to wait, and then tell her you want her to join up. Finally, she'll ask if you want to know her name, but instead say "Let's hurry on." In other words, do the replies on the bottom, then the top, then the bottom, then the top, and so on. She'll then come with you, and can be added to your party any time using the PHS.