Quote Originally Posted by ~Storm Ninja~ View Post
Even if "clone" is a botch by sony, there are two distinct points that are unexplained of this is true.

1. the existence of 2 sephiroths
Sephiroth 1:

Quote Originally Posted by Ultimania Omega Guide
5 years ago, Sephiroth fell into the Lifestream holding the head of Jenova, going to the Northern Crater, where the Planet's energy is concentrated, and where he would begin the Reunion -- and assuring his restoration -- by focusing through Jenova's cells. This regeneration was to be carried out by way of the Reunion, as the scattered Sephiroth Clones (-->P.213) would begin migrating toward the Northern Crater.
Sephiroth 2:

Quote Originally Posted by Ultimania Omega Guide
Shortly after Cloud was apprehended when he broke into the Shin-Ra building to rescue Aerith, the Reunion began. Hojo expected the headless main body to be the focal point for the Reunion once it began, but in reality, it was the Northern Crater. The scattered Sephiroth Clones and the main body of Jenova within the Shin-Ra building all began to move. Jenova shattered its containment case, murdered President Shinra, escaped from the Shin-Ra building and began to wander the world. Now, Jenova's mimic abilities caused the main body to take on Sephiroth's voice and appearance, which it kept hereafter during its appearances in various places.

2. the connection between cloud and sephiroth (primarily illustrated by mind and muscle control)
Cloud have Jenova cells inside his body, and Sephiroth can controll Jenova cells to make the Reunion. Because of this, Sephiroth can manipulate Cloud and influence him.

if you choose to specify the second as bull, I would ask why sephiroth wouldn't just control someone else, say for example, tifa, to get what he wants, or better, make cloud do what he wants by blackmail. There is some distinct connection or reason for his exclusive control of cloud.
Sephiroth can only controll people that have Jenova cells inside of them. This is why he can controll Cloud and the black cape guys, but not Tifa, or Red XIII, or etc.

This thread has a lot of contradictions. Since many of us haven't played in a long while, and probably have fleeting memory of the complex story, I suggest someone finds a website and provide some evidence via a link or reference.
I suggest that you play the game again, and read the Ultimania Omega Guide created by SE, here:
http://faqs.ign.com/articles/698/698416p1.html