The body still carries the patterns of mountains and rivers, but these patterns differ from those Zheng Yichen saw on the hand of the Ancient Venerable. The patterns from the True Immortals' hand depicted flourishing prosperity, whereas these people bore the marks of extinction and destruction.
They are not corrupt, but something else entirely, still alive, yet their life force has mutated. It's not the decay of corruption, but a transformation into negative vitality.
This vitality imbues these individuals with a strong inclination towards destruction. The first ominous individual who approached was pierced through by Zheng Yichen, whose blood was quickly drained dry.
Before it turned to flying ash, it quickly transformed into corruption. Zheng Yichen abruptly halted the devouring; although the ominous still lived, their life force had mutated, but it wasn't death's decay, it's best to leave it be.
One taste and Zheng Yichen felt nauseous.