An Evil Cultivation Method!
The Living Dead was an evil cultivation method which went against the normal laws of the world which would try to maintain a balance.
Unlike the normal way of cultivation where the cultivator would try to obtain the Spiritual Qi from the world and strengthen their own body and also cultivate in order to increase their lifespan, but would still have a limit to it.
The evil ways of the Living Dead were just way too absurd.
It was because the person who practised such a method would never die.
In fact, right before the death of the said person, they would carry over a certain practice where they would use various methods to forcefully let the soul remain within the body.
And many times the methods were just too evil for anyone to even think.
Ye Qian of course knew of many of such evil methods which were used to make one a Living Dead.