Xande alternates between Libra and a series of incredibly powerful magical attacks, including Meteor and Quake. Your strategy should be based around taking down Xande as quickly as possible, as he will rapidly destroy your party with his attacks if you are not careful - about six turns is all that even the most experienced party can hope to survive his onslaught of attacks. Healing is largely pointless in this battle, as the damage that Xande causes far outstrips even the best healing spells, so it is best to go all out attack in this fight.
3D remake Edit
Xande uses two actions per round to usually cast Haste and Protect on himself. He will also have rounds in which he will mix a physical attack, Thundaga, Firaga, Blizzaga, or even Meteor into this combo. It's best for players to have one character devoted to healing for the entirety of the battle while the rest of the party takes him down with physical and magical attacks.