Divine energy.
It's what Rex had initially thought or assumed the Gods were using.
He knew divine strands existed, and it's the fuel of a God's foundation, the core that made them what they are. But the divine energy was only an assumption. It was derived from the otherworldly power those Lunirich Gods used against him.
And now, not being able to sense what these Godlings were using made him realize that he was wrong.
Since the Lunirich Gods needed to tone down their powers when entering the lower realms, their energy might be degraded into something that Rex or the other inhabitants can sense. In truth, their energy was far stronger and also different.
That's the reason why his senses couldn't pick up the energies used by these Gardeners.
Rex looked down at the choking figure, gasping through a torn throat.
Not being able to sense their energy is a fatal weakness.
