An experiment gone horribly wrong. By orders by the Lord Heir D'en, the Ar'Jaed clan was instructed to manipulate demon essence into creatures that would serve them during times of war. As unnatural beings and created with violence in mind, they became insane and broke out of the clan's stronghold.
Now they wander the land, causing havoc where ever they go. Though efforts have been made to eradicate them, they are now able to twist the minds of other demons into copies of themselves.
This is the Zeleth's raw form. A mass of energized gems, all that is needed is a soul spark for it to grow.
Essence
Once a soul spark enters the crystalline form, the crystal shatters as the demon takes on a more incoporeal form. This is the demon at its most vulnerable; when presented to Viscasi, she may add other items to influence the adult form.
Adult
An oddity setting them apart from other demons is that the adult form is genderless, having been created by the necromancers.
Elder
These demons are now evolving as they go; they have managed to make it into Elder status which was unimaginable to the Ar'jaed.