My initial thought on this would to create an Illusion/Storm Defender and take the Stealth power pool This would give you the ghost like powers of spectral wounds, summoning ghosts (phantom army), terrorizing your foes(spectral terror), and whispering evil thoughts into their ears (deceive). With Storm, you can get all the eerie environmental effects of a a ghost - wind, rain, thunder, lightning.
I might second guess the stealth power pool though because you get invisibility with illusion and stealth with steamy mist but it is the only way (I think) to get Phase Shift.
If you don't want the Storm power pool for the eerie effects, since you weren't really talking about a dead person type ghost, I would consider empathy or kinetics.
