Here are the hidden characters in Final Fantasy VII. Below details how to them to join your party.
Getting Yuffie in the party
Yuffie can found in a random encounter in any of the forests around the world. After fighting her, do not pause or use the save point. Talk to her and answer her questions with the following responses:
Yuffie: “You spikey-headed jerk! One more time, let’s go one more time!”
Answer: Not interested.
Yuffie: “You’re pretty scared of me, huh?”
Yuffie: “I’m really gonna leave! REALLY!”
Answer: Wait a second!
Yuffie: “You want me to go with you?”
Answer: ……That’s right.
Yuffie: “All right! I’ll go with you!”
Answer: ……Let’s hurry on.
First you must open the safe in the mansion in Nibelheim.The combination of the safe is Right 36, Left 10, Right 59, Right 97. Be prepared for a battle! After the battle you get a key that opens the locked door in the basement. The locked door is at the top of the tunnel you walk through in the basement. Vincent is in that room hiding inside a coffin.