So William ordered his four monstrous weapons to continue expanding the hole, even if they had to dig directly through the sides of the existing hole they dug already.
He didn't want to waste more time to expand the hole from the surface all the way to the bottom. So he let them form pillars to support the ground above the space they dug while waiting for them to expose enough rocks to reveal this mystery.
And during all this, Fang kept releasing his deadly lightning attack one time after another, while taking five minutes rest in between.
At the same time, all the high-end masters in this underground space saw what Fang was doing. They saw what William's monstrous weapons did, but didn't get what he aimed to do first until the lightning fell from Fang, and lit everything on the ground bright silver, white, and blue.