First off, SM, "TC" is "Captain," and I just added a T at the beginning for the hell-of-it. *goes to edit*
Now, as Phoenix said: Sephiroth is NOT special. He is a normal human being who was injected with Jenova cells since before he was born. All the powers that he had as he grew was the direct result of Jenova cells. Sephiroth's ONLY special powers came from Jenova cells. If only a small amount of her cells can make a human that powerful, how powerful must Jenova herself be?
The black-cloaked dudes you find throughout disc one are, indeed, Sephiroth clones. It has been speculated that the Sephiroth you chase throughout disc one was a successful Sephiroth clone, but there's also two other theories with just as much proof(if not more) to back it up.
