I agree, I had assumed that the amount of Undead one could raise would depend on one's power as a spellcaster. The Watcher, given he not only discovered the Dream but also was quite powerful- would, I'd think, be far more potent with the Dream than someone like the Baron.
Correct me if I'm wrong, but do we ever see Shiver in command of any 'undead' of the typical sort (Thrall, Wights, Ghasts?).
She seems to me to have a lot of Fetch and Soulless, so perhaps she did not have any ability whatsoever. In which case, was this because she was not magically talented? Or because the Dream was something only The Watcher and Balor were privvy to?
LR