I always wondered how the undead stay animated for so long. One thing that has to be a part is that the power of their master must control them and keep them alive. To do this they must be extremely powerful, especially to command legions at a time.
So it must be representative of power, so that a shade can control a limited number of undead of their own, while a Fallen Lords or Avatara can control many more at a single time. I'm not sure what exactly occurs once the power faids or they are killed though. I'm sure that the undead don't just fall over, I guess the power used to reanimate them eventually wears off and they slowly die (again).
Any powerful magic user can use the Dream of Unlife, so there will always be undead. It just depends how powerful they are to determine how many there will be.
Sincerely,
Pimpy™
