Physical flight.
Xu Tui had some understanding of this. Shen Jiushuang, Xu Tui's teacher of the genetic ancient martial arts, had once mentioned this to him. Not all Genetic Transmutation Realm experts could fly with their bodies. However, those who could fly with their bodies must be Genetic Transmutation Realm experts!
In other words, the two people who were rushing toward Xu Tui were both Genetic Transmutation Realm experts. They were of the more powerful Genetic Transmutation Realm experts.
Xu Tui's eyes were filled with coldness as he watched the two Genetic Transmutation Realm experts rapidly approaching him. The person who was targeting him behind the scenes was really willing to spend money. Or rather, he really understood Xu Tui. He actually sent two Genetic Transmutation Realm experts instead of the Genetic Evolution Realm.