Mephistophelean
Mephistophelean (? o?) , proper adjective
Pertaining to, or resembling, the devil Mephistopheles, “a crafty, scoffing, relentless fiend;” devilish in character or aspect; crafty; showing cunning or ingenuity or wickedness; as, a mephistophelean glint in his eye.
Also: Mephistophelian