What do I need to beat him?

I heard of something called Knights of the round, where do you get it?

you need a golden chocobo to get it. its at some island which isn't visible on minimap. it can kill sephiroth with 1 cast.

KOTR and Destruct materia if you want to be sure of killing him.

Yes, you indeed do need a Gold Chocobo. Take a look at the "Sexy" Chocobo breeding guide on this forum. Everything is there except that you can feed it more than 10 Sylkis to boost the stamina.

Get a gold chocobo and go onto the ocean, go to the north western corner of the map (you should see goblin island first)
Its a round island, simply go up it and into the cave and get knights of the round.

W-summon from the battle arena in gold saucer will help you greatly, and also if you got w-item during the midgar mission that will help.

KOTR is a great summon materia yes, but also very cheap. I think they designed it for 2 purposes. 1 for people who really suck and can't win without it, and 2 for the weapons. I don't use KOTR unless up against the weapons cuz it's just cheap and can kill just about anything in one cast. I kinda takes the fun away from beating the hard bosses.

Originally posted by barret.wallace
Get a gold chocobo and go onto the ocean, go to the north western corner of the map (you should see goblin island first)
Its a round island, simply go up it and into the cave and get knights of the round.

W-summon from the battle arena in gold saucer will help you greatly, and also if you got w-item during the midgar mission that will help.

Roflcopter..... Thats 500mp used in one go =D

Though you REALLY don't need KOTR to beat Sephiroth.

You don't need KOTR to win against Sephiroth...

The time to spend to get the summon can be used to level up;
a very useful materia is 4xcut, if u are high on level with that materia Sephiroth will fall in no time ;)

where do i get golden chocobo?

Well there's 2 ways to get a golden Chocobo. 1 is to breed it and as Pacific said it has it's own thread so look there.

The 2nd way is harder. You have to go to the man in Kalm and give him 3 items 1 and book (forgot name) from morphing a Ghost Ship in the underwarter reactor and 2nd a Desert Rose, which you get from Ruby Weapon and 3rd, the Earth Harp (I think it's called) from Emerald Weapon.

Though I reccomend the breeding option cuz it's mighty hard to beat the weapons with out KOTR and even then it's still hard.