Marvel Mystery oil is just that a "mystery" but don't mistake it for oil - it is a cleaning agent.  No scientific proof but I'm pretty sure it is basically Varsol (90%) masked by coloring and a perfume to disguise its true identity.  You can add a little to your gasoline and even oil if you like but don't expect it to provide the lubrication needed that 2-cycle oil gives you in a premix.  Lycomings have been eating Mystery oil for years but its purpose is to help remove or prevent deposits on valves ...
Jeff

People use Marvel mystery oil?
- Matt Boiteau