The first moment that the sage put his numerous plans into action was a long time before he met the serpentine world god for the first time. There was also a long period of planning before that time. During that time, the serpentine world god didn't even know that the sage existed. The sage on the other hand was silently observing and profiling him. So the sage has all the advantages in their interaction. The serpentine world god's caution right now when they are in the thick of things is just the futile grasping of a drowning man.