Please note that due to a significant overhaul of the races during Age 68+69 (2015), this information may be out of date. Please refer to the in-game guide http://alliancesatwar.com/races/ for current information.
It is difficult enough to see a spirit, but to kill one? What a spirit really is, is a little bit of a mystery. It is long thought that they are the cursed souls of the Nazgul. Lacking a physical form brings its advantages, but it also brings its disadvantages.