As I see it, there are 3 differing but related definitions for "Mary Sue":

Even superheroes can't get by without a little help from their friends.

Or, how Kevin Levin learned to relax and love snuggling.

PG; gen; Crossover, crack, blatant metaing
The Doctor embarks on a rescue mission for a young Time Lord lost in another universe.

The Yorozuya trio gets an unexpected reward. They really should've checked their daily horoscope before accepting: Beware of Greeks bearing gifts, don't count your chickens before they're hatched, and be careful when life seems too good to be true, because it might be a sign that everything is soon going to go very, very badly.

Mokuba has a cold, and both he and his brother have some recovering to do. -gen, Kaiba brothers fluff-

Eleven defining moments in Kevin Levin's life so far.

When tragedy befalls Kaiba, Yugi and his friends fear such a devastating loss may be too much for him, and now, unless he can fight a hostile takeover, he stands to lose Kaiba Corporation as well. Or is something else wrong?

Teaching parapsychology is something of a fascinating endeavor in itself. I admit, I get some...interesting types.

Peter and Egon are kidnapped by a madman. Cue the angst! Complete with psychosis-inducing hallucinogens.

A man's home is his castle, and Napoleon and Illya are laying siege on one another in a fierce, relentless, and very silly war of retribution.

PG; gen, angst; tag to 4x11 "The Gurnius Affair"
Four years is a long time. But this is not Napoleon's decision to make anyway.

The boys, stuck overnight on Random Ice World # 69-But-Who's-Counting (Except McKay), just trying to stay warm.

It's not that Radek is afraid of the infirmary, but he doesn't usually have much reason to come: the four-month mandatory check-ups, occasional refills on his migraine medication, and to visit a sick or injured colleague, now and again. Most commonly it's to confer with Atlantis's Head of Science, since McKay is there on a semi-weekly basis, and not always because of his hypochondria. Sometimes he's in one of the beds and sometimes he's sitting beside one, and Radek's mostly gotten used to arguing over the noises of medical instruments, has become practiced at lowering his voice as to not disturb the patients, even if Rodney neglects that caution.

PG, gen angst; "Miller's Crossing" tag, set between "This Mortal Coil" and "Be All My Sins Remember'd"
A little while after "Miller's Crossing," John has a conversation with Jeannie about what transpired.

(AU) A tale of two unlikely friends. (And even more unlikely oni.)

234K | completed 8/01 How much would you do for a friend? The Keeper and Hobbes risk everything to save Darien from his worst nightmares... Invisible Man

35,156 words | PG-13 | completed 4/07

(6th season, angsty h/c) Lex, forced to his last resort, comes to the Kent home, and Clark must rise to the occasion, as he finds himself questioning his assumptions about his dying enemy.
All the Difference

Lex has vision, a reason for everything, and a lot to drink.

fic by X-Parrot

[complete] An experiment gone awry sends Kaiba through time to unexpected, unacceptable future.

"According to popular belief, going more than three days without sleep means you're legally insane. Mokuba's kidnapped, Kaiba's losing it, and Yugi and his deck are just trying to help..."

Missing scene from Miller's Crossing

"Oh, sure, riders said that dragons never hurt humans, but had anyone who believed that ever taken a good look at those teeth?"

by x-parrot A Constant Struggle, 1/2 {6,610 words} PG-13; AU futurefic, Static Shock x-over; mild Clex and V/R Robert and his boys are invited over to family dinner with Lex Luthor and three generations of Kents.

Lex is kidnapped and it's Clark to the rescue as usual, but he might not be ready for all he finds.

Sentinal/Highlander/Gargoyles/X-Files?

(Static Shock crossover, Clex and V/R slash) Having the world's number one supervillain in his office doesn't exactly make Robert Hawkins' day. And that's before they both get kidnapped.

24K words | completed 8/05

(Static Shock crossover, Clex and V/R slash) "Give it up. They know."

PG, SGA/Pern fusion
"Go—go Impress somebody else!"

Almost All Grown Up by xparrot
"Inspired by all those wonderfully fun AUs where Teyla and Ronon are from Earth along with the rest of the team. Turnabout's fair play, I thought."