I do not see a connector to support Mixpanel however a google search turns up some third party solutions you might want to try. In addition, you can create an idea here - Ideas or consider creating one yourself if skills allow.
Best of luck
I was really hoping someone else may have had success building a basic connector for Mixpanel, but I ended up building a python script to export the data from Mixpanel and dump it into a MySQL database. I then connected Tableau using the native MySQL connector. Not ideal, but it works for now.