Chen Mo had previously obtained a mythical-grade equipment called Stellar Shift.
It had an Active Effect!
When activated, it caused all damaging effects targeted at the holder to act on the target itself for 3 seconds. It had a 30-second Cooldown and could be activated even while in the inventory.
The effect of Death Withering was to cause damage equal to 12% of the target's maximum life value each second.
What would happen if I used Stellar Shift to redirect this damage?
This was because SSS-level BOSSes in instances were completely immune to percentage-based maximum life value damage inflicted by professionals. However, they weren't immune if they inflicted such damage on themselves.
Many BOSSes with similar self-harming Skills would damage themselves for a certain percentage of their maximum Health to use some powerful Skills.
When they used these Skills, their Health would indeed decrease.
This immunity only applied to Skills used by professionals.