Theme Mentor - helper plugin for WordPress, the cousin of Theme-Check reporting other possible theme issues
Theme Mentor is quite similar to Theme-Check. It iterates all .php files - your root theme folder template files and your includes in inner folders (plus functions.php).
Different checks are being run to ensure the code quality of the theme. Theme-Check is more or less trustworthy, it does report valid theme errors or missing features most of the time, but it is missing most of the eventual issues in a theme.
What Theme Mentor does in addition is reporting everything that might or might not be suspicious. The average success rate is about 70%, but it serves as a reminder for common WPTRT review remarks for you to double check. After all, you don't lose anything. If you verify the report from Theme Mentor, you would either: a) confirm that your code base is in tact, or: b) fix a nasty error that Theme-Check is afraid to report (fault tolerance issues).