The defining traits of the Yu Liu mechanism series lay in "Dao Gives Birth to One" and "Wave-Raising Flow."
Dao Gives Birth to One was the Casimir effect, the formidable ability to wring spiritual energy out of nothingness.
Then there was the ability to infinitely amplify the slightest disturbance within a circulating flow. In common terms, "a butterfly gently flaps its wings, only to trigger a storm in some faraway place."
When Yu Liu mechanism beasts beat their wings, the chaotic spiritual energy system they created could infinitely magnify the errors within most spells, ultimately dissolving the vast majority of them. This chaotic spiritual energy also naturally blocked spiritual senses. Furthermore, once the Vacuum Infinite Sea was moved, the resulting changes in the spacetime metric naturally prevented Void-Piercing Escape Techniques such as interspatial travel that relied on the properties of spacetime itself.
There was one more point. This was also highly effective against spiritual senses sustained by spiritual power.
Wang Qi had once relied on this, using the hundred thousand Yu Liu Wu mechanisms Mi had given him. With the cultivation of Foundation Establishment Realm Great Perfection and Yue Luo Liuli's power, he had forcibly counter-killed a group of Dividing the Spirit cultivators. Wu Chengdao had also intended to use this trait to restrain him somewhat.
And now, Wang Qi was using this trait to forcibly create an environment outsiders could not peer into.
"Is that... the Control Arrow Technique?" Wu Chengdao had some skill himself, so he naturally saw that Wang Qi's press contained far less power than the Vajra Jiedi mechanism beast. The reason he could hold down Vajra Jiedi was because he had used a control technique to shift all of Vajra Jiedi's force underground.
The rising "curtain walls" had likewise been created by using the Control