Sorcerer

Sorcerers were the Nobodies of Xemnas, who appeared in The World That Never Was.

They projected fields around themselves, and were resistant to magic, leaving the Keyblade the only way to kill them.

Stratagy

The magic Cubes that the sorcerers use can make it hard to get in close for an attack and to make matters worse they have no reaction command. The battle can be quickened by using Reflect at the right momment to deal large damage. A well timed reflect can destroy a Sorcerer in a single blow.