Just like what he did earlier, if one began to hit a wall in the same place with the same strength, then in time, things like this would accumulate and cause serious damage.
Theoretically, even a needle should be able to break down a mountain in thousands of years, maybe millions.
So Galthor used the lesser miracles in reinforcing ways. He created a large air bubble in the sea that instantly sucked out the water and pulled in the masters.
That stopped their drowning immediately, but it did nothing to save Galthor from the jaws of death. But he wasn't done. With the remaining lesser miracles, he created something else.
The air bubble hardened; it then grew bigger and formed into a box several meters wide. It was hard enough that they could feel as if they were standing on solid ground.
Then a force pulled the water serpent directly into the box, straight into the path of the angry masters. Galthor had spent all of the accumulated lesser miracles, but it was worth it.
