I found it. Meng Chuan—who was standing atop the water surface—was delighted.
The most important thing when killing a Sixth Tribulation forbidden creature was to find its Life Core!
A Life Core could be anything. For example, a ship, a flag, a wine cup, a drop of blood, a grain of sand, a blade of grass, a corpse, a mountain, a star, a mystic treasure… Everything could be a forbidden creature's Life Core. Furthermore, it could be disguised. There was nothing special about it when disguised.
This made defeating forbidden creatures easy, but completely killing them difficult.
Meng Chuan deliberately pretended to be weak because he was afraid of scaring the forbidden creature. If he revealed his peak Sixth Tribulation realm strength and killed the other party's true body, his opponent would be so scared that they wouldn't dare condense their true bodies outside of their Life Core. How could Meng Chuan find a Life Core in the vast Chaos Turbid River?