Those are notes, the elf Gaelath Bizeiros made, while venturing in the dangerous Ruins of Sep Ethal.
The most important information I can glean from this book is one of the most adored creatures of this cult. They call them the "shadow wanderer". Probably created by their strange god and just as evil. A kind of monster that can move through the darkness by crossing the line to another dimension and walking right there to reappear where it pleases.
There are some chosen ones who are given a mark of this being. A deep black coloring of the skin. Most of the subjects die if they get marked, but those who do not perish, receive abilities that are very similar to those of the shadow creature. Not that powerful, but quite practical. I'm a little jealous, but the death rate is clearly too high for me to undergo such an experiment. But whoever received a “mark of the shadow beast” was considered a great fighter and was almost worshiped like a god himself.
So the way I understand this ability, you can hide in this shadow dimension and if you focus on interacting with the material world, you can reappear in the vicinity. But you are not completely protected. If a being knows where the Shadow Warrior is, it can still attack it. This ability also has its pitfalls, but I haven't been able to decipher them yet.
So: whoever is here after me: if this shadow beast exists, stay away from it! And maybe there are others besides the beast who have such skills. And if we should ever meet, I'll be happy to tell you more about this cult.