When we reached the location of the Blue Core, Grenol and the others were standing far apart from each other. They figured out the way how the darkness or the fog of war works.
The Blue Core is just a big crystal glowing in blue light. It emitted energy which formed a circular barrier around it. Upon reaching the 100-meter mark around it, we will be subjected to a buff that strengthened us to 10% of our base stats. Although they couldn't see the real value, they could feel it coursing around their bodies.
Moreover, there's someone among the freed Transcendents whose Transcendent Pathway involved incorporating System-type properties. Through that, he informed everyone about the buff's total value. If I have to guess, he awakened some kind of system closely related to his Spirit Pathway.