Then the situation became very clear.
Jiang Lu had once seen the past through Emperor Yin's spiritual river, from the first-person perspective.
Emperor Yin was dissatisfied with Jiang Lu's tyranny and sought to remove him secretly and usurp the throne to establish a Netherworld more to his liking.
But at that time, Emperor Yin was still weak. In a direct confrontation, even if Jiang Lu were to bind his own hands and feet, he would still not be a match for him.
Hence, he searched everywhere for a way to weaken Jiang Lu and, as perseverance yields success, he did indeed find one.
He discovered a poison in some Ancient Ruins, which was said to have once sealed an Ancient Evil God. Of course, it has now been proven to be specifically concocted by Nyarlathotep and hidden within the ruins, intentionally allowing Emperor Yin to find it.
The core of that poison was actually based on the Ancient Gods' artifacts designed to target the properties of the Old Gods.