Deception
The "Parasite" demonic trick allowed Mark to absorb the Mindpower of others through vines that grew out of his hand. Additionally, if the target has zero Mindpower, he could invade into their body, effectively using them as a protective shell or "second life" for himself.
He liked to call that Parasitic Invasion.
It was an interesting sub-ability of his demonic trick: Parasite.
As Hailen watched in horror, Mark's real body grew somewhat immaterial and Mark vanished into the other man's body like a ghost.
Hailen thrashed about, screaming hellishly. Choi Sung watched from the side with wide eyes.
Inside Hailen's mind, Mark and his Souls were combating each other for control over Hailen's body—and Mark, being a demon who devoured souls, easily dominated Hailen in no time.
Calmly, the effeminate young man's cold black eyes fluttered open and 'he' stood up.