I had Asenath Mason’s book regarding (Goethe’s) Mephistopheles then later I found Dr. Johannes Faust’s Magia naturalis et innaturalis where MephistophIEL is mentioned. For me Mephistophiel is the only legit one. I had contact with him. It is written in the mentioned faustian book that Faust made a pact with Mephistophiel for 24 years and had to die after ten years pact.