Vasco

Best answer as chosen by Asker / Ratings
1. You'll need alot of things, but here they are:
Ultimate Recipe: During your final visit to Twilight Town, while you're unlocking the pathway to the World That Never Was, you'll gain access to the underground computer area. The recipe is in a chest just before the pod room. You CAN come back and get this if you miss it.

Ultima Weapon: 7 Orichalcum+ (can be found in:)
1 - Finish Atlantica.
2 - Finish 100 Acre Wood.
3 - Chest at the Brink of Despair in the World That Never Was.
4 - Clear the Goddess of Destiny Cup at Olympus Coliseum.
5 - Chest at the Sunset Terrace in Twilight Town.
6 - Chest in the Central Computer Area at the Space Paranoids.
7 - Collect one of each of the other 49 materials. The Moogle gives you an Orichalcum+ automatically.

1 Orichalcum (Bulky Vendor or chests, eay to find)
1 Mythril Crystal (you need to make it)
1 Dense Crystal - Berserker [12%], World that Never Was
1 Twilight Crystal - Assassin [12%], World that Never Was
4 Serenity Crystals - Assassin [4%], Berserker [4%], Samurai [4%] and Sorcerer [4%], World That Never was.

2. To be honest there is no easy way to beat him. Unless you are in level 99 you can't make mistakes, because if you do, you're death. Take an advice: find a strategy and keep to it and get the Ultima Keyblade.. Watch this video:

Http://www.youtube.com/watch?v=a4m3dLJsHp4

It helped me alot. Now don't expect to win at the first try. It took me about 10 times in level 80. And after beating him, don't save the game. Trust me: you'll want to repeat that battle.

And I've just made my longest sub ever, so hope I helped