Vexen will be participating in tether scanning, power tests, and strange cases testing.

Powers-wise, he's a remarkably powerful mage with an incredibly strong affinity for ice. His dubiously extant nature also makes it all but impossible to injure him without magic.

As for strange cases...his body is literally made of the raw essence of Nothingness, and only exists because his will is imposing form and substance on it. Without his soul present, his body back home would have dissolved into loose magic and disappeared.