Quote Originally Posted by The Crystal
No, he sicks Jenova on his enemys. Why don't use Jenova's body to FIGHT?
Umm you fight Jenova's body.

Quote Originally Posted by The Crystal
During half the game Sephiroth controlled her body, but everytime that he have to fight, he throw a piece of the body to fight for him, and run away.
Yes he controlled her from the northern crater. So therefore you fight Jenova who had changed her body to look like Sephiroth's.

Quote Originally Posted by The Crystal
Then, in the second half of the game, he is hiding in the NC, protected by a energy shield.
That is because he is using his energy to stop Holy from working. And he needs to make sure no one can interfere with his plans.