I thought about that last night, actually; my idea is splitting ghouls into two types:
* Ghouls use the current graphics, but weak stats (say, on par with levies). They'd form Ghoul Lord leaders who have lower stats (maybe half the current Ghoul King stats).
* Armored Ghouls would be ghouls in run-down armor (broken leather, green copper/bronze,). They'd have the stats and leaders that current ghouls have, but would not show up until a certain amount of time passes in the game.
Fortunately, since they work the same, 90% of the coding is already there.