Vessel Manipulation is a process by which a being's vessel is tampered with to one's advantage. This was used by Crowley on Lucifer's vessel Nick before he forcefully summoned him into the body.
Crowley informs Lucifer that Nick, his former and current vessel, has been bewitched, which essentially makes it Lucifer's human prison. Crowley used various unknown spells to improve the vessel, making it strong enough to contain Lucifer indefinitely. He has also incorperated runes and spellwork found in the cage's material into the body, carving it into every molecule. This imprisons Lucifer within the vessel, unallowing him to leave it. There is also a device that was placed into the DNA of both Crowley's and Lucifer's vessel, which allowed Crowley to gain control of Lucifer and his powers.
Lucifer is informed by a demon that the system built into the vessel that enables Crowley complete control over it was designed by Spevak, who had long been killed by Crowley in order to protect the system's secrets. Lucifer hopes said demon can crack the system and free him from Crowley's control.
The device that is used to let one being have total control over another has he ability to suddenly reverse. The true form of the device is not shown, as it is planted into the DNA of both bodies. For an unknown reason, the device can glitch and transfer the power control from the controller to the target.