Devilish

[Sarah]

Resembling, characteristic of, or pertaining to, the
devil; diabolical; wicked in the extreme.

[Luis Fok]

A [personality trait] that would describe the person who possesses it to be cold, mean, or sly; most times the person being described in this sense will at first appear normal, contrary to an outright jerk. Used to describe a [troublemaker] or [sadist].

[Justin Bieber]

[Evil] and [cruel].

[Kai]

Like or appropriate to a devil in evil and cruelty.

[Zipporah Schumaker]

evil or morally bad: