He fallen ones are a unique breed of true demonic origin, one of the few that I’ve been able to conclusively verify through sources other than the ancient Vizjerei tomes in my possession. (How I came by said tomes will, of necessity, remain my secret.)
As my readers are well aware, early Vizjerei writings are often little more than self-serving propaganda aimed at whitewashing heinous deeds committed by the mage clan. For instance, we now know that the goatmen were unwitting human victims of an ancient Vizjerei power struggle for more detailed information on the khazra’s tragic history), whereas the ancient Vizjerei texts would have us believe that they were actually demons – lieutenants of Baal, no less!
Through diligent cross-referencing with other manuscripts in my vast library, however, I have ascertained that the Vizjerei depiction of the creatures known as the fallen ones is factually correct.
As hard as it is to believe, the fallen ones were once exalted demons of the Burning Hells. They served as Azmodan’s hands, performing acts that he would not, could not involve himself in. They were the instrument of Azmodan’s first failed attempt to usurp power from Diablo and his brothers, and after that failure, the fallen were subjected to the full wrath of Diablo. They were twisted into small, ridiculous imps, in contrast to their previously powerful forms. Moreover, if they expected Azmodan to reverse their condition, they were sadly mistaken. The infuriated Azmodan held them responsible for the Prime Evils’ continued reign, and so he left the fallen in their new bodies, where their degradation would serve to amuse him for all eternity. Their failure provided him with the information he required to succeed in dethroning Diablo and his brothers – the event now known as the “Dark Exile” – but that fact did nothing to soften his heart toward the fallen.
When unleashed upon our realm by their master, Azmodan, these impish terrors display a tendency to swarm like flesh-hungry locusts, and they have been known to tear apart a sleeping village in minutes. Small of stature and simian in appearance, these creatures possess surprising strength and unnatural agility. Other than feasting on human flesh, the only act that gives these unspeakable horrors pleasure is breeding; hence the tendency to encounter them in large packs.
However, due to their small size, cowardice appears to be one of the chief features of this species. They quickly retreat when one of their brethren falls in battle.
Fallen ones display no obvious tendency towards greater organization beyond their predisposition to swarm. This is fortunate for humanity, for they are so numerous that if they were to band together in large numbers, they might easily overwhelm a small city.