Half dead might not be entirely accurate, but two-fifths dead is certainly an apt description.
The Longevity Realm cultivator of the Daluo Taoist Lands, after receiving a slap from Chen Zhixing, lost four or five-tenths of his cultivation. By this logic, two more slaps of the same kind would basically mean the end for a person.
Three slaps for one Longevity Realm! Just ask, isn't that terrifying!
Of course, that's a joke. Few Longevity practitioners would go head-to-head with the Dharma Image of the Emperor Ziwei Venerable. Even Yimiao would suffer from such an encounter, let alone others.
It's like a martial arts tournament where everyone is fighting barehanded, but you step on stage wearing half-skeletal armor. Who would dare to stand against you!
