Ice Glass Bones.

Shi Lang dove deep inside the pond, he had to swim quickly because the cold was freezing him, not only his blood circulation was slowing down, but even his consciousness was slowing down. The effect of the chilling water was somewhat similar to the flame wind in the Volcano Garden. 

He figured out one thing, these trials were designed to test the mettle of the body and soul in various ways. While the flames agitated his soul, the cold was slowing it down. 

He had to circulate his spiritual energy at a quicker pace to make sure that his body handles the stress from the cold. His body had been purified to the limit and the frost was corroding it. Thinking about it, Shi Lang stopped circulating his spiritual cultivation sutra, but focused on the flame manipulation technique.