The Branded Poison originates from the 7th rank magical beast "Poison Imprint Serpent", anyone who kills the Poison Imprint Serpent is "cursed",
with the Branded Poison. It has been shown that the Branded Poison can be suppressed by Dou Qi.
The Branded Poison seems to have a will of it´s own. It has also shown the ability to evolve and adapt, this was shown by the Branded Poison when it became more violent after a year or two, since it was constantly being feed Dou Qi, which was originally intended to suppress it. Afterwards it was seen that the Branded Poison could control Dou Qi itself, it was also shown being able to shapeshift. It could even corrupt/corrode Dou Qi elements, such as ice. This shows that the Branded Poison isn´t something to fuck around with.
It is said that the only way to expel the poison (not cure it expel it), is to use a essence flame and a Receptarier. This shows how powerful the Branded Poison truly is. It´s also shown that not even the 19th ranked essence flame can destroy it. Since even though Xiao Yan put all of his power into a attack against the Branded Poison, it simply infiltrated his body instead of perishing in the fight. This shows it´s both clever and powerful. It is unknown if the Branded Poison is simply bidding it´s time, or waiting to regain it´s former power. Xiao Yan mentioned that the Branded Poison was under his control, and that the Branded Poison has an incredible destructive power.