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.

showing the cunning or ingenuity or wickedness typical of a devil; "devilish schemes"; "the cold calculation and diabolic art of some statesmen"; "the diabolical expression on his face"; "a mephistophelian glint in his eye"