Right away, cast Aeroga. Whenever it runs out, cast it immediately. In the
first part of the fight, Sephiroth only does normal slashes, teleports around,
and uses a magic attack that cast 4 pillars of fire around him. The fire attack
covers about 1/4 of the arena, so when he does that, Glide/Superglide away or
use ARCANUM. (Arcanum makes you invunerable during the attack, so you won't
take any damage and since Sephiroth is in the middle of a big attack, he can't
teleport away.) Sephiroth jumps around alot, so be sure to have him targetted
because if he is behind you and you don't know it, he can cause a whole lot of
damage. Sephiroth is at a slight disadvantage from aerial attacks, so jump at
him and then let loose with a combo. When Sephiroth's life is down to about,
half of his red bar, he'll start jumping more and then when he stops and waves
you towards him and says, "Come", he's about to use Sin Harvest. (Send
Heartless Angel.) After he taunts you, he'll teleport again and glow a dull
pink. At this point you should Superglide at him and attack him as fast as you
can. If you failed to attack him in time, you will have a halo around your head
and all your MP and all HP except one will be gone. Use an Elixir quick! (NOTE:
If you don't have Second Chance equipped, Sin Harvest will KILL you in one
hit.) This is the second part of the fight. Now, Sephiroth runs around
incredibly fast and teleports almost twice as much. Just attack him with
ARCANUM or manual combos like you did before. Try to use your Elixirs only when
he's successfully cast Sin Harvest. After his life bar is brought down to his
yellow bar, he'll be in his third and final stage. Now, there's good and bad
news. The good: He only casts Sin Harvest about 1/6 of the time. The bad: He
can turn invincible. He'll start off by using a move that is very much like
Omni-Slash. Just press the Guard button EVERY half second to minimize the
damage. Then, he'll go to the center of the Arena and step into a black/green
thing. This turns him invincible. Then, he'll cast an Ultima type attack.
Little blue orbs surround the arena, so stay about almost halfway in. Don't try
to attack Sephiroth because he's invincible and those orbs fly towards him.
Then, he'll cast Meteor and those will spin around the arena for awhile. Again,
just heal and sit this part out. When he stops that, he'll attack from the air
with a spinning move, swinging his blade the whole time. Just use ARCANUM so
you can meet his attack with the pain on him, instead of you. Whenever he is
running around the arena, he's got a trail of orbs behind him, so watch out and
don't hit them. When he's got about half a green life bar, he'll actually
attack a little less and go back to taunting you. Just keep doing ARCANUM and
you'll put him down for the second time.