The original, often used, often parodied plot framework to be associated with Mary Sue, exclusively featuring the female Purity Sue dynamic. It's what a lot of people think of when the term Mary Sue is brought up.
Mary Sue Classic is perfect. Everything she does is perfect and everybody knows this. She may or may not acknowledge this (after all, you can't be too humble), but deep down in her (perfect) mind, she's the most aware of everybody. The heroes can't seem to find any topic of conversation but how wonderful (and perfect) she is and the villains can't help but have a grudging respect and secret lust for her. In a high school setting, she's that one girl that every guy wants to date.
She can't help but cause men to fight over her (perfect) presence. However, with a (perfect) word, she can convince anybody that she's too (perfectly) good for them and make them fall in place. She might come across as prudish at first as she resists the charms of the hero (or, perhaps, the Ensemble Dark Horse), but she'll succumb in the end. Once they're together, everybody else who was competing for her (perfect) charms will accept it because they want her to be happy. They won't even be jealous. Instead they can express their smittenness through Courtly Love and swearing that they're dying to do her (perfect) bidding.
Her (perfect) goodness is so powerful that her very (perfect) presence changes the world for the better. With a brief (perfect) plea, she can make the villain give up his evil plans and settle down to a life in service of the better good. Perhaps he doesn't expect to ever be good enough for her to consider him, but just the fact that somebody so pure and special (and perfect) exists is enough for him to try to make the world the perfect place for her to live in. Wars end when she gets involved, with both sides realizing the futility of killing each other and striving for a (perfect) future together.
In spite of the implications of this perfection, premarital sex is hardly taboo for her. She never has casual sex, though, and certainly never has many partners. She'll often sleep with her one true love after they've made their (perfect) relationship official, but it's not uncommon to see her redeem the villain with a night of (perfect) fornication. If she's not a virgin at the start of the story, that's because she had a doomed relationship with somebody that was too good to last (or, alternatively, the villain before his Start of Darkness). More often than not, this relationship produced a (perfect) child that seems to be conspicuously absent, usually because of a kidnapping or tragic accident or something (Parental Abandonment is below her, after all). Expect this child to take her (perfect) place in the (not-so-perfect) sequel.
Sadly, it often won't last. Perhaps because she might lose her (perfect) charms if she got old, Mary Sue Classic has a tendency to not make it past her (perfect) twenties. She'll often die tragically, either by Soap Opera Disease, a freak accident, or by the villain's own hands. In the rare case she was not able to reform the villain by her (perfect) words, her (perfect) death will cause him to realize just what a monster he has truly become and repent for his sins. Everybody will show up to her (perfect) funeral (even the villains) and give a speech on how someone as perfect as her was Too Good for This Sinful Earth. As her (still perfect!) body descends into the earth, everybody will vow to continue on the ideals that she had exemplified.
If the story doesn't end right there (after all, what else is the story going to talk about? Those other people? Who gives a crap about them?), it's always possible that Mary Sue Classic will come back as a (perfect) Guardian Angel of a character, easily capable of reforming them or saving them or whatever she's there to do. After they are reformed, she'll ascend again, perhaps after a fleeting (and perfect) kiss on the lips that ensures nobody ever forgets her. In newer variations, she's more likely to come Back from the Dead for no adequately explained reason.
Yeah, one can't help but vomit at all this. Once the most common Mary Sue style story (although authors seem to be catching on now), this is also the most blatantly visible. Usually pops up in amateur fiction and especially fanfiction (where the author simply didn't know any better), it's pretty much the feminine ideals taken Up to Eleven. No doubt inspired in part by Princess Classic, although she need not be an actual princess.
Contrasts Butt-Monkey, a character suffers from everything hilariously.
No examples (perfect or otherwise) here please, this just defines the term.
We apologize that "perfect" doesn't look like a word anymore.