Regular MMO I have found info online saying it contains the following two main ingredients (plus a some anti wear additives in small amounts that I don't have the details on).. I think this specific info was from the NTSB which analyzed and published the analysis of the Marvel Mystery Oil because it was found in the gas/oil of a plane that crashed.
Petroleum distillates--"Hydrotreated heavy naphthenic" Naphthenic Base Oils or Alkylated Naphthalene's are Group V base oils made from distillates of crude-oil (74%)
Petroleum distillates--"Stoddard solvent" also known as white spirit, 10–30% is a paraffin-derived clear, transparent liquid which is a common organic solvent (25%)
I am curious to see how the "synthetic" MMO is made up. Has anyone seen any testing on it yet? I am assuming probably not, if its a relatively new product...