What is pertaining to, or resembling, the devil Mephistopheles, "a crafty, scoffing, relentless fiend;" devilish; crafty called?

mephistophelian — Pertaining to, or resembling, the devil Mephistopheles, "a crafty, scoffing, relentless fiend;" devilish; crafty. (Webster's 1913.)

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