Capítulo 439: Make a Move

Great One Onimbus's Pathway involved him assimilating System-type properties. This method that he made was born from that.

But there's a more direct comparison I could think of to how this worked. 

It was similar to the method the Orc Shaman used back in the Ancient Ruins. That Skill from their book. The Transference of Life Force of the Ruin Dwellers to forcefully induce growth for the young Orcs.

However, here, this method that Onimbus created was using the other natives' Life Force as a fuel to increase one's stats. They weren't squeezed in one use like that Totem-enhanced Skill of the Orc Shaman.

On how many times they could be used to raise someone's UPL, it depends on the natives' strength. If it's a Rank 5 Mortal then around 5 times before one was squeezed to death. Moreover, they needed three bodies to squeeze Life Force from for the method to work.