Actually, a better idea:
Deploro's own.
They are beings from the Overworld that ventured into the Ender in search of the treasure that Deploro promised. However, they were captured by Deploro and they were twisted into beings of evil, their minds cast away into a shadow to be replaced by sinister replicas of Deploro himself. They are rare but deadly, with amazing attacks and unique AI.
This also explains the myth of Herobrine: Herobrine was once an explorer that ventured into the Ender and lost his sanity, becoming the first of Deploro's own.
Herobrine will not be a major part of the mod as he never appears in the actual game, he is only included on a minor bit of Lore.