Xaldin is also really cool. You'll fight him as the Nobody boss in Beast's castle. He is not especially awesome nor especially boring, I do not have strong impressions of him. He uses a set of Six lances, which he uses to attack you, and sometimes, to form a giant snake-like thing he rides and shoots a giant laser at you.
He commands the Dragoons, and he looks badass too, with a evil look, and the crazy hair. in 358/2 Days, he helps Roxas out on his missions...Alongside with Vexen, Lexaeus, Xigbar e Zexion, he used to work in Ansem's lab, (his somebody, Dilan) as is showed in BBS.
You'll battle him in a narrow bridge outside the castle. Try to use the reaction command "learn", to hit him, and stay away when he forms a shield with the lances. In this battle, you can use a trick. If you die, Mickey will appear, and fight him in your stead, while gathering energy to revive you. You can be save quite some times with this, altough it's not really necessary, it's not a hard battle at all, just tricky. When he forms the snake-like thing, run, to avoid being hit by the ray of light.
The last one is the precise part of the battle in which you run, because the wind is a shield to him...