The Tainted Qi Disarray was an Upper Mystical Grade Forbidden Spell acquired by Dargoth from the Central Repository after spending almost all of his wealth.
The function of this forbidden spell was to cause disruption within the cultivation foundation and souls of living beings and corpses alike, and then leave a 'Tainted Seed' of the user almost undetectable by the victim unless they were a full realm above the user.
Once someone is successfully infected by the 'Tainted Seed', the user can then take their time to slowly take over their bodies and souls without them even realizing it.
It was truly a dreadful forbidden spell, and all it cost to activate it was that the user needed to split a fragment of their soul. But that's exactly why it was also dangerous, because if someone overcame this forbidden spell, then the 'attacker' would become a victim of their own spell.
