After Xue Ren killed the spirit mercilessly, he spread out his awareness wide, his eyes going around rapidly. If this world was hidden world of Dragon Lightning God, then there is definitely not going to be a pleasant inheritance.
All because the spirit told everyone that this is place wehre Dragon Lightning God had been mutating his victims.
From Rushai's memories, Xue Ren had knowledge as to how this process is going. Demons had worlds that were purely formed with 'hell's energy' and this very energy would naturally enter bodies of their victims imprisoned in their worlds.
Then using demonic techniques, they would properly brainwaish their victims depending on their attitudes. It's not like every fallen world got their people turned into blood pools and other ingredients.