Mary-Sue Detector

8

Mary-Sues often don't have any motivation for what they do. So what if they don't know why there going on this ridiculously long quest? They're doing it out of the goodness of their hearts even though they have no emotional drive to do so.
Or, if the Mary-Sue is a villain, they're only killing everyone because they want to. No reason why or how they got to doing that— they just do it because they can.