Xadin is extremely diffuclt to defeat, this is what the KH2 Stradegy guide book says:
The fignt against Xaldin is extremely diffuclt. Before entering this battle, equip your entire party with Potions and Hi-Potions. Begin the battle by locking on and jumping in to attack as Xaldin's speed and range are diffuclt to counter. Watch for a chance to get a Reaction Command with each attack. Because its so diffuclt to get in close against Xaldin, start off with Donald and Beast in your party. As the battle progresses and Donald runs out of Potions, swich him out for Goofy.
The Learn Reaction Command is essenital to staying alive and inflicting damage. With each one, you will earn a Jump Reaction Command that replaces a typical attack. It is possible to hold more than one Jump, so don't miss any reactions. Unloading a number of these consecutively is great for catching him off-guard. After knocking him out of his offensive stance, pile on the Air Combos. The more powerful the Air Combo finisher, the more likely you will keep him off his feet.
Quickly run away if he starts to glow green while attacking. (i refer to this as his "tweak mode") This means that he has entered a berseker-like stage, and it can result in instant death.
Any time that Xaldin flies away on his spears, run down the bridge as far as possible to avoid his wind attack. Fourtunately, King Mickey is here to help out as long as you dont give up. King Mickey cant defeat Xaldin on his own, but he can restore Sora with his Drive Gauge.
As far as Drive Forms are concerned, both Valor and Master probide power and speed advantages (i suggest master) , but neither will bestow the damage of the Beast's Limit. This is a great way to finish off Xaldin.
Get bonuses are- a MAX HP increase for Sora, Donald + Beast, as well as the REFLECT ELEMENT for Sora, and AUTO HEALING for Donald.
k hope i could help u out.