Where do the Illborn come from, and what do they want.The Illborn are creatures from the various universes that co-exist in the Multiverse(Mostly, it seems from the Universe where Haria Exists.), which have foolishly entered the Warrens and had their souls torn out of their bodies; and rendered a soulless husk of their former selfs. Humans which have their souls torn out seem to just become limited to certain characteristics for the rest of their soulless lives, living lives of simplicity. The Siblings may also possess the ability to mould the Illborn into specific templates, mostly based on real creatures, or creatures from other uniiverses. They are said by the "Feeding and Care of Mercenaries" to lack true feelings of emotion, as those probably lie within the Soul itself. For example, Slog was always a hungry orphan child, who only ever thought of food; when he became an Illborn, he could only think about food, and most likely nothing else.(And the only time he has exibited true sentience was when we gave him food.)
They are non-hostile to most, unless aggrevated, provoked, or directly controlled by one of the Siblings.; the only exception to this seems to be Al, who is described as a "free soul" during Ciro's Rebirth. The presence of a soul must anger the Illborn due to either:A)Instructions from Siblings to hunt down individuals who possess a soul, so it may be processed by Oric. B)The presence of a Soul just angers them, and they wish to steal it for themselves, like Heartless and Nobodies with Hearts.
Illborn are a limited in their ability to become stronger, as they lack a soul. This is seen when we scanned Slog for information.
The Illborn must be wanting a Soul to call their own, as Al, one of the few(maybe even only) Free Soul in the Warrens is constantly harassesd by the beasts; They must believe they can tear his Soul out of him, so that they may once more feel true emotions.
As described by Slog, when he had his Soul torn out, and he saw it, he felt happy and at peace, and he could see everything that was him inside of the Soul; but when it was taken away from him, he felt like he was trapped, vulnerable and deserving of his Punishment. Assuming the same process happens with every other IllBorn, we can conclude that the other Illborn are just lost, soulless creatures; who are condemned to the Warrens for the rest of their lives.
The only Odd Illborn we have seen was CoolCrab, but based on these conclusions, cool crab must have been 500% cooler when he had his soul.