Kingdom Hearts II I need help.

Help with the Data forms of I, VIII, and X.
Or
Xemnas, Axel, and Luxord.

They pwn me.

 

I don't have the game but I have been watching a few videos so I could still give advice. I only know the Axel battle though.

This'll be easier if you're either having alot of healing items for HP and MP and are ready to spam some MP costing attacks, or having Ultima Weapon.

At the beginning of the battle move back a bit so his summoning Fire Ground doesn't kill you. When it is summoned, Go ahead and mash down Trinity if you'd like. If not then move away with Dodge Roll to dodge a few of his attacks. Hit Overtaker ASAP or your HP will go down and you might quickly die with Axel bashing you down. I'm not sure, but Blizzard might do some heavy damage. Try it, maybe spam it. Just hit Overtaker as much as possible. Heal if your HP is low.(Duh xD) When the screen darkens(Limit I think) Then Guard or dodge roll. Guard worked for me in KH2. Use Limit Form and mash down on them KH1 moves xD You'll kick him down.

That'd be how I do it, Keep moving and don't let him wail on you too bad with the Flamming Ground.

Don't take my advice for granted although, Like I said, I've never played it.

 

Axel.
Avoid the Summon Fire that he uses right away and try to sneak in a combo. Eventually, your health will drain. Auto-Shift into Limit.

Spam L1+Circle and get the finisher for it. Axel will be thrown up into the air and will then jump into his wall of fire. Run around in circles (it's important that you're moving or you won't the command; stay away from the walls, too) and mash triangle to the get the reaction command that removes the fire-floor. He's stunned now so try to get two of Limit Forms Ground finishers.

When he starts moving again, use L1 Circle again. KEEP doing it. Eventually he'll summon the fire floor again. This is fine because even if you don't do damage (he makes himself invulnerable for his desperation attack), mere contact restores some HP.

Eventually, you'll get the Limit's finisher on him and he'll leap into the air and out of the arena. Reaction command again and finish him off. (If you don't by now, just keep doing L1-Circle. Each single hit counts as a finisher but be aware that you can't beat him unless the floor is normal. Throw him out again and get the reaction command again.
Reward: Magic Up.

Luxord.
I really thought I'd have a problem with him so i saved him for last. Oddly, i did it in one try. VERY luck based, IMO.
Spam Thunder whenever he's far away and ignore his card games. When thunder hits he'll flinch a little. Nail him with a finisher. Keep that up until you're clearly ahead of him. So long as you're casting thunder to start with from a safe distance (and keeping in mind that thunder disrupts his attacks) you'll quickly gain a lead.
Eventually he'll use his desperation move. Try to get each counter to land on a circle. If you fail, Luxord DRAINS time from you and gives to himself. Not a big deal though. Assuming you survive the drain and survive through your dice form, he'll eventually try again. Success, not matter how much time he has left, will always drop his time to ZERO. Basically, just keep trying until you get the last game right. IMO, luck based.

Xemnas 1.
Guard right when the battle starts and keep guarding until he's done his combo(s). Throw some combos on him afterwards.
Xemnas 1 likes to warp around the field. Time it right and you can deflect his arrival and nail some combos. if all else fails, guard again until he stops.
I've also found that Limit Forms L1-Circle (I love that move, honestly) works pretty well, too. Just keep doing it.
At about three bars of health or so, Xemnas will start the building sprint reaction command. Run over the building and press triangle. If you can, while the sprinting up the building scene plays, watch for the reaction command to change three times and hit the third one. Manage then and Xemans lands stunned with 1 HP. Finish him off.

Xemnas 2.
Xemnas 2 is the real challenge. Thankfully, Riku joins you. Be sure to go to TWTNW and equip him with Hi-Potions to use on himself and you (that's about all he can really do for you) and to give him some half-decent armor and accessories.
Don't bother trying to attack when Xemnas throws you up into the air with "We shall go Together". Just mash triangle until it's over.
Now, you can try the Limit Form abilities here if you want, but when Xemnas starts his regular laser barrages, you'll want to have Reflect, so revert.
Xemnas is very fond of standing in the middle of the stage and throwing giant balls of energy at you. Glide around and see if you can sneak in there to attack him. he stops the attack eventually, but a finisher will do that early.
Be relentless. He sometimes shows up and splits himself into two. Big deal. Pick the real one and beat the crap out him.
At some point you'll gain control of Riku. IGNORE the Xemnas clone and take a path around him to reach Sora. In other words, don't be-line it to him. Take some strides diagonally left or right to help avoid the Xemnas clone. Mash Triangle as you get closer to him and free Sora.
You'll prolly familiar with the last of Xemnas' moves: The super-long laser barrage. Circle-Triangle-Circle-Triangle-Circle-Triangle-Circle-Triangle over and over. Survive it and you win. Be aware that it lasts a bit longer this time than it used to. You CANNOT win until you survive this attack. If you get him down to 1 HP and he doesn't use the attack right away, KEEP YOU DISTANCE. You don't want to die being so close to victory.