(a.k.a. The Seething Eye)
Some say that the blood-shot eye of Karx'oleth sees everything. At the very least. its followers can feel it in their head at all times, and it can open up as a third eye in their foreheads. The more its presence is felt, the more eyes will appear everywhere. And every eye of Karx'oleth can open up as a maw, devouring the souls of those nearby. It doesn't seem like Karx'oleth can be truly destroyed, but it is locked away in the Far Realm. For now, at least. There are those insane enough to seek its favour, promising their loyalty and souls in exchange for some of the entity's power. There are no documented cases of this turning out well for those making such a bargain.
General Physical Condition
Karx'oleth is almost completely defined by its ever-searching eye. Its body is a seething mass of tentacles and thousands upon thousands of smaller eyes that open like hungry mouths instead of blinking. The size of the being is incompressible as it bends space around it to the point of seeming infinite.
Karx'oleth might be older than creation, have formed during the First Breaking, or not exist within time as most understand it at all. There are no accounts of it until after the Second Breaking, but that might be because it was hiding better rather than not being around. The large claim to fame for Karx'oleth is being one of the five entities behind the Sunset. It was the eyes that watched every attempt to save the world. It was always watching, always ready to claim the souls of those who opposed it. Only the direct light of Amaunator and Selûne delivered straight into its eye managed to blind it long enough to make the Sunrise happen.
Even compared to those who would claim some similarity to Karx'oleth, it is extremely paranoid. If it can't see something, it assumes that it's dangerous and must be obliterated. This insane paranoia and desire to break into every mind makes it much more dangerous than mere cunning ever could. You can never outrun Karx'oleth. You can never hide. Not even your thoughts and mind are safe from it.