I think there's one more significant trait of a Mary Sue you failed to mention, and it's less to do with the character than with the setup of the world. Number nine touched on it, but...things work out for Mary Sues. They're not forced to face the consequences of their own stupidity or bad decisions. Even if they're wrong about something, they're not really wrong, because it will turn out, through often impressively implausible twistings of plot, that they were really right.
Something I've learned, in reforming my MSes, is that you can change the character around all you want, but if you the author still have the same attitude toward him/her, the character will inevitably twist back around again to MS territory. It's another level of meaning to "murder your darlings." Step back and let your characters fail. Let them be unlikeable. Let them be occasionally stupid. And let other characters call them on it. Let the consequences of their mistakes drop right on top of their perfectly-coiffed heads. Let other characters chew them out and be right, and let them react to such chewing out with ill grace. Make yourself write a scene employing some part of the character's personality that you personally don't like very much. And if subsequent edits mean you have to get rid of that scene, write another one.
None of us like each other all the time, and none of us like every single thing about any of the rest of us. I find that's a really useful fact to keep in mind when writing.
no subject
Something I've learned, in reforming my MSes, is that you can change the character around all you want, but if you the author still have the same attitude toward him/her, the character will inevitably twist back around again to MS territory. It's another level of meaning to "murder your darlings." Step back and let your characters fail. Let them be unlikeable. Let them be occasionally stupid. And let other characters call them on it. Let the consequences of their mistakes drop right on top of their perfectly-coiffed heads. Let other characters chew them out and be right, and let them react to such chewing out with ill grace. Make yourself write a scene employing some part of the character's personality that you personally don't like very much. And if subsequent edits mean you have to get rid of that scene, write another one.
None of us like each other all the time, and none of us like every single thing about any of the rest of us. I find that's a really useful fact to keep in mind when writing.