New units in Necropolis. Discussion and selection between upgrades.

Both upgrades are quite good and practically comparable in terms of characteristics (ghosts are slightly more initiative, while poltergeists are slightly faster and tougher), and their incorporeality helps them equally. The only choice is the ability: they are both usually not used very often, although casters still have to be attacked, and to steal spells, it is enough to approach within movement range and use the ability. However, spirits still recover well from stolen mana, but poltergeists haven't figured out what to do with spells yet. Perhaps, in the next patch, this aspect will be refined.