if you look around their should be some spotting of shadow from the moonlight, when they enter into this area they should take on their less necrotic form and be vulnerable to attack.
Defeat Sephiroth.
What boss.
there is a great guide at supercheats.com
Sephiroth is an extremly powerful enemy. he is the drak side of cloud basically. In kingdom hearts you can defeat him in the collusem but only cloud can truly defeat him.
You have to hit its hands.
you suck there ear
defeat the small jellyfish in atlantica
Living Bone
You have to defeat Cloud in the Hercules cup.
nobody knows
By beat the life out of him
Not unless you replay the game.