So it's been a while since I really had a topic that I could sink my teeth in to and give some credible thought to. This topic was actually brought up to me, I was asked my thoughts and I didn't have time to answer right away. So Becky, this post is mainly over your question. Heh.
What is a Mary Sue/Gary Stu?
The classical definition is a character created by a writer in order to influence the plot of their work, with pretentious, superfluous, powers or characteristics that have little basis within the confines of the character. Wikipedia defines Mary Sue/Gary Stu types as being Wish-Fulfillment of the Authors. However I find that most clinical definitions are made in such a way that they don't fully express what the whole issue is. Mary Sue is a term that covers a lot of things. Wikipedia has a very detailed break down of all the various connotations. Which I love. However those tend to be based upon -writing- for books, not for roleplay.
So. Let's get with the Roleplay Breakdown.
Within the confines of Roleplay, a Mary Sue is a character whom is still wish fulfillment for the Mun. It's a character who fills some void for the author in a way that is almost perfection. Most of the time the character has overblown, unrealistic for the setting, powers or abilities. Which are rarely explained in any manner that makes them truly 'fit the setting'. A good example of this is a character being thrust in to a foreign setting where most of the characters in the game are perfectly normal average, real people, perhaps a noir setting. However the Mun creates the perfect woman, she has perfect breasts, perfect eyes, the perfect body, and the writer will often take two paragraphs of 250 words or more describing why no sane man (or woman) within visual range would ever do anything but stare and bow down to their feet.
Within the confines of a Noir Setting, such a thing simply doesn't fit. Everyone has flaws. Any woman that visually perfect would be marred with a history of drug addiction, sexual abuse, and/or is probably permanently an indentured servant of the local mob-boss. The Author simply PUSHED that character in to the setting out of their own selfish, infantile, desire for attention that they themselves lack in real life. What they're really saying is "LOOKIT ME! I'M A BEAUTIFUL UNIQUE SNOWFLAKE!"
This goes for men too. Marvel's Sentry? Is a Fanboy's wet dream, and the biggest Gary Stu that was ever invented for a Marvel Comic title. He's such a Gary Stu that a lot of fans buy books with him in it, just to see what absurd thing he'll do next that would NEVER be allowed from any other character in 100 years of comic books.
On the other hand, a Mary Sue or Gary Stu can go the opposite direction. You know the character. I know you do. It's that one character that nothing ever goes right for. Let's see if we can just be the most emo-tastic, fucktard, in the whole world. Can anything else go wrong? Sure it can, stab the guy with hot knives! "LOOKIT ME! I'M NOT A SNOWFLAKE AT ALL, I'M ANTI-SNOWFLAKE! NEENER NEEENER!"
Within the world of roleplay I both loathe and love Mary Stu-ish toons. I love them because most of the time if you just try to ignore that one toon? Then the mun will play their other 15 toons amazingly well. I loathe them because, well.... I'd rather punch myself in the testicles than have to smile and nod one more time when someone else tells -me- how unable to resist -their- character's natural charm and charisma I am. I love them because this gives me an insight in to the person, their flaws are exemplified in how wish-fulfilling their character is, so it gives me a natural read upon the mun. I hate them because for no rhyme or reason a Mary Sue will alter the setting to fit their whims ( I saw someone in a room on IB once post that their character was so pretty even the Enchantress had expressed jealousy. What? WHAT!!?! The Enchantress... jealous...?! /wrists ).
In short my dead Mary Sues and Gary Stu's, I have one bit of Sage Advice for you: Fuck You Snowflake.