Phantasmic Air is an ancient technique that was long lost in the Mortal Realm. This techniqus was only usable once one was at mid-Deity Transformation stage. It was vastly demanding, but could temporarily seal someone inside a spatial tear. The tear didn't exist for long and couldn't be entered from the outside.
The efficacy of the technique would depend on the cultivation of both the technique's target and its caster. Dissolving the technique itself also required an immense amount of magic power and a powerful spiritual sense.
This technique also went by several other names such as the Immortal Seal Curtain or the Nightmare Prison.