Mephistophelean vs diabolical

Mephistophelean

adj
  • Showing the cunning or ingenuity or wickedness typical of a devil. 

diabolical

adj
  • Extremely wicked or cruel. 

  • Of or concerning the devil; satanic. 

How often have the words Mephistophelean and diabolical occurred in a corpus of books? (source: Google Ngram Viewer )