With sephiroth what you need to get down is the pattern.
I usually beat him cause I have a tendency to stick close to him, so when he is about to do that angel thing I'm already searching for him.
As long as you have elixers though you should be fine.
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So if i put it in this way does it make a difference.
When the last light fades, the dark being will rise to control the world, we will al fall before him the mighty Barney.