Noah and June didn't initially intend to go at it so intensely, but the sixth floor's reaction proved their approach right. Nothing happened when they replayed the various passages of the dual cultivation performed in the past, but everything changed when they lost themselves in their passion.
Gabrielle had given energy to the mountains when she cultivated, but something entirely different happened while Noah and June expressed their feelings. The rivers, sandy ground, grass, and waterfalls lost power as something began to take in the underground world.
Noah and June didn't completely understand the reason behind that reaction. They had theories, but they stopped caring about them once they saw that their approach was working.
Old Tyrant, Gabrielle, and the turtles imitated Fiery Mountain and retreated on the other side of the dark world when they saw that attacks were piercing the black crystals. Nothing reached them, but they didn't want to test their luck.