Since nobody else had anything to offer worth reading, I'll help you out. This is a tough mission if you try and play it "legit." There are going to be a ton of hallowed knights and wizards coming at you and you'll likely get overrun. If you want to beat Xyor and don't mind the boredom, your best option is to set the Pagoth free and then hide in the room behind the room with the Shrieker until Xyor pops in. The Shrieker won't bother you and for the most part neither will the minions but they will all come to the Shrieker room to find you. Hit Xyor with as heavy a fire weapon as you've got and you'll complete the bounty. You don't have to do anything more than kill him and then you can go back to orbit.