Through his conversations with ghosts, Jiang Li learned quite a bit about the Underworld. There were ten rulers known as The Ten Halls of Yama who governed all affairs in the Underworld. Beneath them were the Black and White Impermanence, the Horse-Faced Ghost and other infernal officers who were all Ghost Immortals.
The Underworld was filled with innumerable Ghost Immortals who could battle against the Immortal Realm.
The Underworld managed the spirits of the dead and had little interest in matters of the living world.
There were many Immortal Artifacts in the Underworld, all related to the cycle of reincarnation. The absence of any one of them could potentially disrupt the cycle of reincarnation.
All this information aligned with what the old immortal had told him.