Earlier, Yun Xiao did not deliberately hide certain details. The reason he didn't take action immediately was indeed some unresolved problems he was pondering over.
These problems weren't theoretical but rather related to Yun Xiao's current Meridian Qi Cultivation or, more precisely, the level of his Meridian Refining Technique, because after all, he was merely a Low-level Heavenly Stage Pulse Refiner.
If it were just some Low-level Heavenly poisons, Yun Xiao could have easily neutralized them without even needing to use Little Dragon's "One Thought to Solve Myriad Poisons" method.
It was the thought of having the magical Dragon Tree Spirit Little Dragon that enlightened Yun Xiao, making him realize how he had forgotten about this convenient son. Little Dragon's detoxification methods were unparalleled in the world.
