Last night a friend of mine produced the best high-concept definition of the Mary Sue I'd ever heard:
The singularity around which the story is forced to bend.It's not going to replace the more sustained analyses of this phenomenon, but it sure is a handy introduction. And for a practical guide to available countermeasures, Teresa Nielsen Hayden is right to recommend The Game of the Gods, in which the Powers of Middle-earth play a game of Sues:
Varda smiled. "Your move."Excuse me while I go chortle for a while ...
Morgoth flinched. Then he looked over the board in front of him. It might have been a chess board, save that a chess board didn't have many flashing blue and green oblongs on it, and wasn't covered with ivory pieces showing various girls and young women with their faces frozen in expressions of longing.
He tapped one of the pieces, a human girl with pointed ears and cat-shaped eyes who sat in front of an oblong box. She flushed pink and then began to breathe.
Varda looked disappointed. "That one? She will be easy to dismiss."
Morgoth smiled smugly. "She is a Sue. They are never easy to dismiss."
"When I am allowed to apply reality to the game," said Varda, "they are."
Some moments passed in silence, which didn't cause Morgoth to flinch, and starlight, which did. Then he said impatiently, "Aren't you going to do anything?"
Varda smiled mysteriously. "Reality is enough."