First and foremost is their scale. With the advancement of his cultivation, compared to before, it has expanded more than ten thousand times, able to accommodate more evil spirits and countless dark creatures.
After all, over the years, it's not just evil spirits imprisoned in the Hell dimension; there are also numerous dark creatures, Essence Devouring Beasts, and so on.
In short, the Hell dimension has essentially become a super prison.
It is mainly responsible for sealing away terrifying monsters that the Immortal World finds difficult to handle.
Of course, if these terrifying monsters die in the Hell dimension, the energy from their bodies will be absorbed by the Hell dimension, thus becoming a part of it entirely.
This can significantly increase Zhou Sui's cultivation.
Even if the energy contained in these monsters doesn't match that of an Ancient King, they win by sheer numbers.
If accumulated, it would be no less than numerous Ancient Kings.
