Hidden Characters
Getting Yuffie Kisaragi
To get Yuffie on the first disk be in the Junon Area, go into the forest (landscape) the biggest area of it run around in their you might not get her first off but you might fight enemies. It might take even 10 fights before you fight her, then beat her (of course) then you go & talk to after you one this is what you should say to her.
WARNING don't try & save it is a trick if you try to save she will run away.
Question #1: "Not Interested."
Question #2: "Petrified."
Question #3: "Wait A Second!"
Question #4: "That's Right."
Question #5: "Let's Hurry On."
For a much more higher chance to fight Yuffie, Equip A Enemy Away materia (must be mastered to work) get that from the Gold Saucer which can be one from the Chocobo Racing & a Luck plus materia, This will give you a higher percentage to encounter Yuffie.
If you want to get her at the Second disk you do the same as above but you go to Mideel when Cloud & Tifa are out of your party. Email if you can do it any other time all place.
Then you will have Yuffie on your team.
Getting Vincent Valentine
With Vincent you can get him in every disk, at the same place. This How you get him. Go to the Nibelheim Mansion, Go to the safe that is on the second floor (go up the stairs & if I recall correctly it's in the room first right. You can find the clues around the house but their a no challenge finding them. Here are the Combinations of the safe.
Right 36
Left 10
Right 59
Right 97
This means that you can't go past the number 36-37 then go back to 36 or higher or using left directional pad to go to 10 & so fourth but accidentally miss so it goes past 10. Don't forget to press circle button to lock in the number remember you have 20 seconds to do it in & It won't work if you pass the number.
Once you Open the safe you have a monster to fight, maybe when you get to Nibelheim your first time you might experience difficulty winning, but you should have no problem from say disk two onwards. After beating him you will get the Key to the basement & also RedXII Limit 4 manual aswell as something else.
Decent the spiral staircaseand into the coffin room you can now enter with the key. Vincent is in one of the coffins. Talk to him, leave, then comeback & talk to him and as you are about to depart to the stairs he will come running out & join you. NOTE: you have to click on his Coffin about Three or Four times.