How to Defeat Xemnas (Final Form) Battle in Kingdom Hearts 2

Use the abilities. These are the abilities you must equip: Action: All except Guard, Counterguard, Explosion, Trinity Limit, and Horizontal Slash. Growth: High Jump LVL 2 or higher, Aerial Dodge LVL 2 or Higher, and Glide at any level. Support: Scan (Optional), Air Combo Plus (Both), Combo Plus (Both), Combo Boost, Air Combo Boost, MP Rage (Both), MP Haste, MP Hastega (From Ultima Weapon), Berserk Charge (Optional), Second Chance (Optional), and Once More (Optional).

Use Ethers, Curaga, Reflega and Thundaga as shortcuts. Place Reflega on X, because it's probably easiest to use on the X-button.

Defeat. Before you can go to the Final Form battle, you must defeat five to seven other battles, depending on if one counts the first two battles as real battles.

Don't equip any items, except Ethers and Mega-Ethers, because Riku has the Cure Potion ability which heals you, but also drops his MP, so that's why equip only Ethers or Mega-Ethers, since they will be the most useful. You can also buy Ethers in TWTNW Twilight's View Moogle, which is the last moogle in the whole game.

Go to the battle with Xemnas!

Try to save Ethers. Also, try to use very little magic and limits. You can also auto-reload Ethers and don't equip any action abilities, except for Cure Potion, Eternal Session, Dark Shield and Dark Aura, and, of course, your abilities.

After you beat all battles in the final battle, except the Final Form battle, read this!

Use Reaction commands. Xemnas says "Anger and Hate are Supreme" then at that point you will use reaction commands, but watch out if you equipped Riku's Auto Limit!

Use Reversal and try to use action abilities and Riku's Eternal Session to attack him!

Use Reflega. After you take off at least three health bars from Xemnas he uses lasers, so avoid them by using Reflega. He also sometimes stops, but continues using lasers. Don't attack his copy, though. His copy doesn't have any HP.

Be quick. After you take off at least four health bars, Xemna may capture Sora, which is when you must hurry! This is the only time that you can control Riku, without using any cheat codes. You should ONLY use Dark Aura and make sure to move towards Sora before his health goes down to 0. Try to make Sora take plenty of damage because then Riku can use Cure Potion, which gives you more chances to rescue him! You can also try to get the other Xemnas to hit Riku's back, which would move Riku closer to Sora.

Attack. When Xemnas have very little HP left, he makes his ultimate attack! He summons 1,000 lasers, so have both characters use Reflect. The Reaction Command is for Riku and the X button is for Sora. To make this easier, turn the controller sideways and rapidly tap the triangle and X buttons to block the lasers.