You have a cool/sexy/sweet/etc. original character you want to put in a story, whether it's a Fan Fiction or an original story. But you aren't sure whether your character rises to the level of a Mary Sue or not. Perhaps you have written other characters this way, or you're concerned that you might have put too much Wish Fulfillment into the character. Well we are here to help.
The accidental Sue
First, we need to establish a distinction between an intentional Mary Sue and an accidental one. Characters like Jenna Silverblade, for example, are very clearly Mary Sues, but that's what the author wants. Oh, she doesn't want the criticism of the character being called a Mary Sue, but it is clear that the author has deliberately written one. This guide is not intended to deal with that kind of Mary Sue.
The second thing you need to understand is what a Mary Sue is. A Mary Sue is an audience reaction to a series of events that strongly suggests that the author herself is unduly favoring a character by changing other characters or the environment in inappropriate ways. When the audience calls "Mary Sue" on a character, the author has shattered their Willing Suspension of Disbelief. There are a number of subjective points here, which naturally means that everyone's Mary Sue threshold is different. But it does suggest some places to look.
Essentially, there are two basic faults that lead to the accidental Sue. One of them is any form of author/audience dissonance. That is, the author is thinking one thing, but the audience is getting another. The other fault is when the reader hits some form of trigger, a pattern of behavior that he or she personally finds is an indicator of a Mary Sue.
These sound similar, but they are different. The former is caused by the author not properly communicating. The latter is caused by something that is somewhat out of the author's control. That's not to say that the latter cannot be avoided. There are ways to dodge certain popular Mary Sue triggers.
Mary Sue Fear
Before we go too far, you need to honestly answer this question: why are you here? Maybe you're just here on a Wiki Walk. But if you're reading this page for advice, then you probably think you already have a problem. What exactly is this problem?
If you're just trying to exercise due diligence in making sure that your character is fine, that's one thing. But there is a general sense of "Mary Sue fear". This is caused by people looking at a number of Mary Sue tests and thinking that because their characters ring certain bells, they've written Mary Sues.
In general, if you're reasonably old enough to have consumed enough books/movies/TV/other media, you probably have an idea about how a story and characters get put together. The intentional Mary Sue is generally caused by obvious character worship. If you're reasonably mature and versed in storytelling, you can tell when you're clearly reaching into a story and running interference for characters. And if you aren't, then no advice page can help you.
One of the biggest creators of the accidental Sue is the Informed Attribute. It is very easy for an author to simply fail to realize that the character that she envisions is not the character that she wrote. Fridge Logic also gives birth to Mary Sues.
These are the hardest things to avoid. Avoiding them requires looking at one's work dispassionately and considering the implications of what is written, without regard to the characters. Beta readers are a good help for this.
Triggers are more important to Fan Fiction than to original works. Most fanfic readers have developed finely honed Mary Sue detectors. Many of these detectors are tuned to specific fandoms. An original character behaving in one way might not be a problem for one fandom, but in another, it would instantly drive a reader away, screaming "Mary Sue!" the whole while.
However, there is also trust. If an author can get a reader past the first few chapters (assuming the work is that long), then she may be able to start doing these kinds of things. Once a reader trusts the author, the reader is more likely to accept unusual things from her.
The kinds of triggers are wide and varied across fandoms. But there are certain almost universal triggers.
The Big One: A lot of examples on this page can be summed up as "Your character must fit within the established world". Don't create a special character to your personal liking and just corkscrew her into a story; you must cultivate her out of the world you're writing. It is possible to do both at once but you should never ask yourself "What would be a cool character?" before you ask yourself "What would be a plausible character?"
Entitlements. If your original character starts getting things, whether actual possessions or just respect, from actual canon characters too soon after his or her introduction, this will have readers leaving in droves. Even if there is some explanation. Avoid this until some level of trust is formed.
Violations of canon. Every canon has rules. If a character starts breaking the rules, readers are going to call Mary Sue very fast, unless there's a really good explanation that is given immediately. Original Villains might be able to get away with it so that they are more of a threat, but certainly not a new hero.
Romancing canon characters. If the story is all about an original character romancing a canon character, people are generally going to call Mary Sue on that. And those who don't certainly will if a canon relationship is broken up to do it. If any romance is going to take place, it needs to be relevant to the overall plot and contribute to character development, and it can't overwhelm the rest of the narrative.
Overtly flowery descriptions of original characters, as opposed to rather bland descriptions of the canon characters. Most Mary Sue-based fanfiction is poorly written, and thus will contain lavish descriptions of original characters. Avoid doing this early on in a story.
Original fiction triggers.
While triggers are primarily a fanfic problem, there are some for original fiction as well. Politics is a huge one. Generally, people are willing to accept that people behave according to different political views. But if the author starts running interference, erecting strawmen for the main character to fight, then a certain section of the audience is going to cry foul.
The problem is generally when the story proposes to take sides. And even if the story takes sides, things are made worse when one side is treated unfairly. Unless that side is an Acceptable Target, even fair minded people who agree with that side may call it out.
This means the author needs to be able to recognize the difference between the strawman version of an argument and the real thing. If she can't, then she probably shouldn't be getting this political in her work, unless of course, the work is intended primarily to promote that political viewpoint and will be sold primarily to that audience.
Mary Sue causes
Remember that a Mary Sue comes from a series of incidents. There are a number of of incidents that can happen in a story that forge another link in the Mary Sue chain. Doing one of these might trigger some people, but it is not in and of itself a problem. Doing a lot of them, however, can and will.
One of the leading indicators of certain forms of Mary Sues is one or more characters getting something that she has not yet earned. This could be the respect of her peers, some magical bauble, the love of a handsome, amazing person, or something else that we would expect somebody to work hard for, but for Sue... it just comes.
The Informed Attribute is a particularly difficult enemy here. The author can have a character idea in her head that truly says that the character has that attribute. But if it isn't on the paper, then as far as the audience is concerned, it doesn't exist. Sometimes we see the attribute mentioned but it doesn't really show up or affect anything, so we forget about it. That includes informed abilities and informed flaws.
When a character gets something, make sure that she deserves it. Treat extras as characters in their own rights.
Forcing the issue.
Many Mary Sues are born from attempting to force something to happen. That is, the author wants a particular plot point or character interaction to happen a certain way. Or more subtly, she needs to build a scene that shows that a character has property X.
The best way to do these is to try to develop circumstances in which the character interaction will naturally lead to what the author wants to happen. Build a scenario in which property X is naturally revealed by the characters themselves. If one tries to force things to happen against the will of characters, the invasive hand of the author can be seen.
The best way to guard against this is to have a clear character arc for each character. Know how each one responds to certain situations. And make sure that any extras or secondary characters are behaving properly. Sometimes, this means reconstructing whole scenes to make sure that the right character traits are showing through.
The easiest example to show how forcing creates Mary Sues is with a Villain Sue. Accidental Villain Sues are commonly created by well-intentioned attempts to show that certain villains are credible threats to the heroes. The audience may accept one or two contrived circumstances or instances of hyper-competent behavior that allow the villain to pose a threat. But if it happens repeatedly, in different ways and circumstances, a Villain Sue results.
Attempting to make a Xanatos Gambit, for example. A Xanatos Gambit seems quite simple: there are a limited number of outcomes and all of them are desirable to the planner. But the more possible outcomes there are, the more contrived a gambit becomes, the more the author's hand is seen, and the more likely the audience is to see the character as a Villain Sue.
Falling In Love (You, not the Sue)
The author should care about her characters to some degree. But Mary Sues are fundamentally about authoral favoritism. If the author falls in love with one of her characters over the others (particularly for a story about a group), then she's skating on thin ice.
It is very easy for an author to subconsciously push a character into Mary Sue territory when she loves her too much. Think of it like if you had three children. If you loved one of them the most, then the other two would feel pretty terrible.
First and foremost, remember that writing is more than just creating cool characters. Some people like world building, others like to explore relationships, others prefer exploring a certain genre, others prefer to create something that comes from the deepest corners of their soul, while others prefer to make the audiencecry, cower, feel happy, laugh, or pump their fists and cheer. Remember, cool characters don't make good stories; it's good writers who make good stories.
You are writing a story, not building a shrine. And your character is part of the story; the story is not just a part of her.
Don't assume that both the Mary Sue and the Anti-Sue are completely wrong in what they do. If your character is average or non-notable, the audience will come to detest her in a new way - she has no right being at the center (or even side) of a cast of fantastic people, unless she's an Unfazed Everyman.
Don't care about only this character. Care about them all (even if the villains of the story are cared about in a different way).
When describing the character, it should never come across as the author telling the audience to like the character. Unless it's through the viewpoint of a character, in a way consistent with their characterization, avoid using purely subjective terms or comparisons. For example, if the character has long blonde hair, just simply say she has long blonde hair with maybe an added detail or two if it's important. Don't say "she has the most magnificent flowing golden hair since Sandro Botticelli painted Aphrodite on a clamshell". Telling the audience to like your character usually just ends with the exact opposite reaction. In general, follow the "Show, Don't Tell" rule.
It is equally important to avoid editorials when discussing the world's reaction to the character. Saying "Everybody always picked on her, but this was because they were jealous of her" is a surefire red flag that one is not only writing an autobiography, but laboring with a self-imposed delusion.
When giving your character special traits, remember that traits must exist for a reason more plausible than just being awesome. When coming up with your character's history, start with the single most interesting thing about your character - the reason you want to write about this person in the first place - and then work backwards. Create a history for your character that can be described in terms of relatively boring causes and effects of that one interesting thing. Come up with both negative and positive experiences your character has had and personality traits he or she has developed as a result of that one interesting thing, rather than just listing a bunch of awesome but unrelated abilities or character quirks.
Your character should not be able to solve the main conflict simply by his/her mere presence. Stories are about conflict, and a lopsided conflict in the heroes' favor is already an Invincible Hero, and an original character will make that even worse. A character with just the right skills to meet all the challenges the story throws his/her way makes for a boring story, and will draw resentment from the audience.
As a counter-point, don't make her fail at everything as well. A Failure Hero is just as frustrating as an Invincible Hero, if not more so. As the backlash against the Damsel in Distress, Faux Action Girl, and other similar tropes show, the audience doesn't sympathize with characters who mostly cause problems. She should have some level of success to go with her failures, or if she always wins, she should have at least enough difficulties in doing so; find a middle ground that works for the story.
Do not always let your character's perceptions and judgments always correlate with reality. You as a writer will know what's going to happen, but your character does not. Letting her always 'sense' something's true nature, always guess correctly, or somehow know things she shouldn't, means that you're practically allowing your character to break the fourth wall and have a peek at the script. A character is meant to be a person in her own world, not a player-character armed with a cheat-sheet.
One exception is when you're writing a highly cynical or paranoid character suspect a secretly evil character - they will expect the worst of everybody, but remember that these are character flaws and their suspicions turning out right is just a coincidence. Heck, because they're so cynical and paranoid, it's possible nobody will even believe them.
Do not give your character special treatment. She should suffer the trials and tribulations of life just like everyone else in the story. Giving her Plot Armor or using an Ass Pull to shield your character only demonstrates you're just playing favorites. If you honestly can't bear the idea of bad things happening to your character (or have them happen realistically), then you need to learn to not be so emotionally involved - like the saying goes, "Murder your darlings."
If you don't want to "murder your darlings" at all, you can still write a story in which no murder is required: fluff, comedy, romance, or a mix of all those.
Parody Sues are overused. While that isn't necessarily a bad thing, try to keep them out of the spotlight, and more into the realm of Plucky Comic Relief.
And remember: A character that is deliberately designed to be bad is still bad. Pointing it out and snickering at itdoes not make the character better. Although it may improve the story.
When writing what a character is like or can do it is important to know the standards of the universe he/she is in. What may be absurdly impossible in one universe may be common and acceptable in another. Play it safe do the research and follow precedence of the setting and its characters.
Don't intentionally design your character to be the soul mate of an existing character, most importantly don't just make her the female version of a male character. She can be similar to an existing character in some ways but, since no two people are exactly alike, she shouldn't be his equal in every way. Also, her being similar to a male character doesn't necessarily mean that he will like her; sometimes when people are too similar or similar in the wrong ways (ex, they are both very stubborn, very temperamental or very egotistical) it can cause them to grate on each other.
But don't go in the opposite direction and write a Relationship Sue who makes up for all of the existing characters short comings, tolerates (or fixes) all of his flaws and always knows just the right way to respond to his behavior and bring out the best in him, that's just boring.
"Who is your character when she's alone?" Don't define her solely by other characters, their reactions to her, or her reactions to them. Picture your character alone in a room. What is she thinking?
Make sure your character has a personality. You're writing a character, not just having a person do cool things. What does your character like or dislike? What does your character want in life? What is your character afraid of? How does your character feel about the other characters?
Don't just make this character's personality one you think is awesome, and that you'd like to be. Even the coolest characters in fiction have some depth to them. There are often some flaws to overcome, or that not everyone sees these characters as cool. Better yet, don't try to go for a cool personality. Just go for a personality you think would make a great story.
Don't make everyone agree with your character about everything. Unless your character has some kind of mind control, characters are going to have their own opinions. It's the disagreement that makes them different, even the heroes. Conflict is one of the most important elements in fiction, and even your character needs some.
Corollary: Don't make every character who disagrees with your character turn out to be wrong. The protagonist isn't always infallible.
Your character can be cheerful or sad. Just don't make your character so happy or depressed she doesn't have any other depth. Your happy character could be naive. Your sad character could be happy about some things, but they don't show up a lot, and that makes your character sad.
Is your character incorruptible? There had better be a good reason. Perhaps your character gave in to temptation in the past, and this hard lesson made your character now know better.
Mary Sues often have flaws, but those flaws don't matter. Your characters must have personality traits that affect her day-to-day living negatively. That's what makes it a flaw and not some sort of neat quirk that just adds to her badassness.
If you're up to the task, try making a Deconstruction of your character's strengths. Someone with a lot of emotional stamina may be able to push themselves further or fight harder, but she may also be stubborn or short-tempered. Someone who is a great planner may also be a perfectionist and never satisfied with anything until it's absolutely perfect. Take her strengths to their logical extreme and make them a double edged sword.
Additionally, flaws are often made or broken by how the other characters react to them. A character can be as objectively flawed as all get-out, but if the people around her ignore her faults (or even admire her for them), then they don't really count as flaws.
If your character has particular abilities or personality traits - good or bad - then demonstrate them clearly and logically within the plot; don't just have the other characters talk him or her up all the time. Having all the other characters talk about how wonderful or amazing your character is isn't going to make the audience like her any more, especially if you don't demonstrate them; it will in fact probably have the opposite reaction.
Go light on the snark. It's okay to make your character a Jerk with a Heart of Gold, but do remember the "...With A Heart Of Gold" part. She must have some redeeming qualities that make the other characters tolerate her.
Every strength has the potential to become a weakness under the right circumstances. If your character has an enhanced ability, don't just consider the ways that that ability could help them also consider all the ways that that ability could become a hindrance or be turned against them by their enemies.
Also, in terms of skills, one thing that you can do to bestow more realism to a character and edge them away from sue territory is give them fringe powers and weaknesses as well. Let's say the character has an unnaturally or magically high empathy. One fringe benefit is they may become an Omniglot and be able to speak to anybody in their native tongue. The issue could be that they can't fight because it hurts them just as much as the enemy. Also remember to build around the ability's weaknesses and strength as well. The character might be illiterate in the setting because nobody uses the writing system they use, because his ability only allows him to communicate to the person they are talking to, also making them speak in a foreign language when not directly addressing people. Maybe this character is wonderful at dodging because they can sense their attacker's next move. Give them that depth that makes each ability not only useful and harmful, but also how it branches out to be both good and bad, because a sue who's abilities are only "harmful" to them as well as only helpful is still a sue.
Don't give your character skills that aren't important to the story, just because you think they are cool. Even if they don't show up in the story, they are meant to help flesh out a character, not to make her look better.
To expand slightly: Cake-baking skills in a story about a cake-baking competition fit. Cake-baking skills that are used to cheer up another character or poison an enemy (or a friend, accidentally) also fit. Cake-baking skills in a story without ovens or cake do not fit.
Don't make your character better at everything the main characters can do, because then you don't have a character. You have The Munchkin. If you have to, choose one skill from a main character that your character is better at, and make sure this character has a good reason to be more skilled. Let's say one of the main characters is a swordfighter. If this character has only been training for a few years, and your character has been training since childhood, you have a good reason. But this doesn't mean your character replaces that main character, only that your character has more experience in that skill.
Also realize that the higher up you go in education, sports, or any creative field, the more you will hear the saying "talent is cheap". To be the best of the best you need to literally dedicate yourself to something body and soul, and you need to be working at it every single day. There is a reason not everyone is immensely skilled at even one thing, never mind the two handfuls The Munchkin is going for.
Talent is okay in moderation, but don't make your character the best ever. Don't make it "just naturally talented" either. That happens in real life, but it's such a common Sue trait it's best to avoid it. Just make sure that if your character is really good at singing or playing an instrument, the character has had plenty of practice to hone it. Again, this skill should be at least tangentially relevant to the plot in some way.
It's also worth mentioning that even in Real Life, people who are natrually skilled at something still practice daily. Sportsmen practice constantly. Pianists practice constantly. If you want to be the best, you have to work at it.
Few abilities translate as well as you'd think. Driving a car doesn't mean you can fly a plane. It doesn't even mean you can drive a motorcycle. Fencing with a foil doesn't mean you can engage in combat with a katana. Michael Jordan was an awesome basketball player, but he kind of sucked at baseball. One skill may aid in learning another, but it doesn't equal it. Knowing how to play the piano means you can read sheet music and keep time. It doesn't mean you can pick up a violin and turn out a concerto.
In general, it's best for an amateur author to avoid writing about sex. This is not to say it can't be done, but it takes a ton of verisimilitude and a lot of allusion to make it work. One of the pitfalls of many writers with little to no sexual experience is to make major errors through extrapolation on what constitutes "good" sex.
Even if one feels she can do it well, it's also worth noting that the vast majority of stories don't have any real business with a sex scene. If nothing particularly unusual, shocking, or (emotionally) revealing occurs during one, then the author might as well let her readers imagine it for themselves if they're so interested.
Make sure that the skills your character has fit the world she lives in. A medieval girl who knows how to play a lute is plausible. A medieval girl who knows how to play a magical electric guitar, African drums or the didgeridoo is not. Similarly, if your character has no real reason to know a skill, don't give it to her; for example, resist the urge to give your thoroughly non-Japanese character a katana, even if Katanas Are Better. Stretching the story to fit in a convenient swordmaster will not help.
As a corollary to this, don't give your character skills that his or her gender, social class, race, age, species, physical ability, culture, what have you, would prevent him or her from having, unless you can give a really good reason for why he or she would have that skill. For instance, an upper-class girl in the 18th century would most likely not know how to command or sail large ships. Also, if canon characters with similar limitations couldn't do it/learn it, your character can't.
So Beautiful, It's a Curse is largely a Discredited Trope in normal fiction, and that goes double for fanfiction. Don't do it. That doesn't mean your character can't be attractive. Just don't try to make your character stand out by being excessively MORE beautiful (or ugly). Try to make your character's appearance distinct in the details.
If you want your character to be notably beautiful, make sure it makes sense for her station in life, access to cosmetics and the amount of time she has to apply it. A young prince being handsome and neat is much more plausible than if he were a peasant. Saying that he is just 'naturally' pretty and blemish-free despite endless days of working in fields is unrealistic; make sure his background backs it up.
If you think shimmering, violet hair would be cool for your character, but hair like that doesn't show up in the setting, leave it out. If you write the character well, then exotic hair and eye colors (for the setting) are not needed.
Body figures that are atypical to the setting are best left out as well. You want a slim, but attractive character, go ahead. Just make it reasonably slim and attractive.
One of the most important facts of life (and in fiction in most cases) to take into consideration is that what one person may view as "beautiful" may be different from what another person thinks. Love is blind. An average looking character may well look, to their love interest, like the most beautiful person in the world, while nobody else is particuarly stunned either way.
It could be used as part of the plot, for example: The character believes in said viewpoint about personal preference when it comes to beauty, but may also have low self-esteem about her own appearance. The villain can be a Manipulative Bastard and convince her otherwise by praising her beauty, in an attempt to gain her trust, make a Face Heel Turn, and use her as a pawn.
Fancy, ultra detailed costumes had best fit in the setting. A lot of RPGs would allow costumes like that, but Harry Potter would not. Keep the clothing reasonable to the setting. If you want a minor costume quirk, that can often work far better than a bunch of extra frills.
If you are going to spout Costume Porn about the character, make sure this character is not the only one. Although many would like this trope kept to a minimum, reserving it for one character or two is another way to almost instantly make the character look like a Sue.
Odd costumes might make sense if your character's a Cloud Cuckoolander in which case, people might find it more strange or discomforting instead of exceptionally attractive. You'd also have to be prepared to mention why your character continues to dress in a stand-outish way. Does she have a lot of cultural pride, or has she not had sufficient time to adopt more local manners of dress, or is she compelled or required to dress in the exotic fashion for some reason - perhaps due to being part of some kind of cultural exchange or diplomatic mission, in which case dressing in a foreign style could be seen as "waving the flag," so to speak.
Colors should be kept tasteful and plausible with the setting and its culture. If a culture really only has access to dark red cloth, a character wearing a bright green outfit breaks suspension of disbelief pretty quickly unless there's an in-world reason (i.e., they spend time abroad, or were raised in the manner of another country, or belong to a mercantile family that has access to foreign cloth/dye and styles). If the motif is unspecified, odd, intense colors like bright pink, magenta, purple, and such tend to be noticeably unusual. The exception would be if the character's lack of taste is an actual character trait instead of an unintended side effect.
Do the research. That's what the Internet is FOR.
Realize that there is a drawback to having a Pimped-Out Dress, wearing a corset, and putting on anything overly flashy in general. The upper classes were able to get away with this sort of stuff because they had the money and the time for it, and didn't have to do manual labor. The flashiness was used to signify class and to intimidate others - not for being useful. If you are aiming for realism, don't expect your heroine to be able to fight with a sword when wearing a ball gown*
, run away from pursuers through a thick forest with her Rapunzel Hair flowing free behind her, or pass as a peasant without taking her huge bling and showy makeup off first, because stunts like that are just plain unrealistic, and should get her killed. If your character's running around in an outfit that draws attention, it's very likely to draw the wrong kind of attention... unless that's what you're going for (like a sheltered princess who doesn't realize that going alone in the marketplace, while wearing a lacy silk dress and a cape linedwith fur, will make her a target).
If you're unsure about what might be plausible in a story and it's not too extremely dangerous, try it out. Want to know what type of heels are best to run in without breaking? Try a brisk walk or jog in your favorite pair. Think your girl can run a marathon in a properly-tied corset? Find someone who sells them and ask if you can try one on, with them helping you tie it. Or, if you can't do it yourself, ask someone who has. The internet isn't the only place you can do research, though the answers could easily be there.
Let your characters get hot, sweaty, dirty, messy and pasty if the situation calls for it. A person should not have a 'light sheen' of sweat after running a marathon. Watch some sports (triathlon coverage is good) and see what people really look like after exertion.
Always remember, when describing a character: do we really need to know that her eyes are emerald green? Would the character be so fundamentally changed if she had brown eyes, or a slightly harder chin, or heavier eyebrows than you envision? Admittedly, sometimes the answer is yes. But remember that a story isn't about what the character already is so much as the deeds she does and emotions she feels, and what she looks like is a very small part of what she is.
That said, one or two distinctive details can help make a character real in the reader's mind, as well as give some foundation to attach a name and actions. Names alone can get jumbled up - especially if you start adding Loads and Loads of Characters - but it's a lot easier to keep track of them when you picture them as "Julia, the green-eyed girl with the freckles," "Timothy, the shaggy-haired guy with the perpetually deadpan expression," or "Robert, the lanky guy with the crooked teeth." But what you SHOULD avoid at all costs is something like: "She had thick rimmed emerald eyes that seemed to have a ring of deeper, verdant green in the center, brown hair that gleamed a thousand different colors of autumn and a tiny, porcelain nose dotted with wide-spaced light brown freckles." You should also describe the character only about once - people aren't going to forget what she looks like halfway through.
Note that oftentimes, characteristic actions can be just as evocative, more interesting, and possibly even more relevant to the story than distinctive appearances. If a girl has a peculiar habit of quietly appearing in a scene without anybody noticing her arrival, or a guy tends to scratch his beard when he's thinking, that alone can give a solid foundation for the reader's imagination to build upon, without ever having to mention hairstyle, clothing, the occasional scar, etc.
If your character is a non-human with drawbacks, such as a vampire, don't allow her to circumvent or ignore them unless the series makes it possible. Introducing a plot-device like a magic amulet so she can go out during the day is also very risky, especially when the canon stipulates that no such thing can exist. Even if it can, it could still leave a bad taste in readers' mouths if no one else has such a thing*
An exception would be if that item is the MacGuffin in the story, and it might even be more dangerous for your character to possess it than any benefits it would give
Make sure your character is physically capable of performing her skills. A normal teenage girl would not be able to snap a grown man's neck with one hand, defeat everyone in a bar brawl, or dodge a bullet. Obviously justified in a series with superpowers or magic.
Assuming your character has an ability that would allow it; a telepath may be able to read someone's mind from across the planet, but he's not likely to survive being flung against a cliff by the opposing team's muscle unless someone intercepts him or it's just a low-reality story.
Always be aware of your character's physical limitations. A character should not be 'just fine' after a days-long trek through the desert, nor should an unenhanced warrior, no matter how hardened, be able to fight for hours without getting tired. Again televised sports (boxing, Olympic wrestling, or mixed martial arts) are a good way to see what the results of physical exertion look like.
If your give your character a physical flaw, make sure that it's relevant enough to be brought up. A character being prone to asthma attacks after lots of physical exertion is definitely important. A character having a wonky tooth is not, unless it has a major drawback; maybe missing a fang causes others of his kind to consider him an outcast or coward, or lacking the tooth means that her beast-form is at a disadvantage due to loss of a tusk/fang/the power said tooth might grant if whole.
Be aware of what scars actually look like, especially in regards to the medical attention they receive. A lack of timely or competent medical attention causes ugly, colored scars, meaning that a pirate should not have a thin, delicate scar over his eye after being attacked with a rusty old sword. If someone is injured during a flight and said injury never gets proper medical attention (beyond binding it up), it'll heal badly and should definitely impede the characters - Through sheer pain and potential bleeding up to infection and even amputation if it's bad enough.
If there's a Big Bad in the fandom who always kicks the canon's butts (except in the season finale), your original character cannot beat them herself. She just can't, okay?
Additive: If there is a reasons the Big Bad is so strong against the characters, but might have a weakness that's uncommon in the area it takes place in, it would be more believable. However, even with this excuse, remember to put limits on it. Why would the character be carrying around/ know how to use the weakness? A foreigner healer who somehow knows how to summon elementals which the Big Bad would be weak to is just as much a sue issue as if the sue was from the area. If the big bad is weak to healing, maybe Revive Kills Zombie or he has wounds which give him power so long as they don't get healed, then it would make sense for this character to have the means to take down this otherwise all powerful figure.
Magic jewelry is okay if it is common in the setting. If it's rare, or is hardly ever worn as jewelry, you might want to reconsider.
Having a cool vehicle should also fit in the setting. If the main characters don't have their own individual rides, your character shouldn't either. And even if everyone has his or her own ride, your character's should simply be unique, not better. A Bugatti Veyron would be ludicrously unbelievable if applied to Initial D, for example, because that would be a balance-breaking vehicle; a Cadillac Deville would be a much better choice, being a large American car in a setting populated with Japanese sports cars.
No laptops with wireless unless they actually exist in the setting. Same with any other gadget. No iPod exists in The Eighties. Your character may have something like a Sony Walkman.
Give your character only one weapon, a pair of weapons that are often paired together (pistols, daggers, etc), or a primary weapon and a plain backup weapon (an ordinary short sword for the archer to defend himself with in close combat, for example). A character with a magic sword, a pair of Abnormal Ammo guns and a magic whip is implausible and going too far. The exception is the setting has everyone armed to the teeth, as in a combat-centric story centered around the military, mercs, or large-scale battles.
If your character is in a world where most swords have special powers, be very careful about giving the character's sword the same power as the main character(s). This is especially true when the main character's sword is supposed to be unique, like Excalibur.
If your character is a time traveller, anachronistic accessories are acceptable. At the same time, always remember the limitations of the era the character is visiting: An analog-capable cellular telephone might work, though not without problems, in the 1950s, and will work in the mid 1970s, but not the 1920s. A gun will work anywhere, in any time, but replacement ammunition could be hard to come by. Technology Marches On in all fields; even so simple-seeming a thing as a dry cell battery changes over time.
Canon Character Relationships
It's fine for your OC to have a significant connection to an existing character, but make sure it's a plausible one and that it doesn't interfere with that characters previously established personality, image and back story (ex: if a character is established as a misanthropic loner who's never experienced real companionship, don't make your OC his beloved best friend from back-in-the-day that he just happened to never mention before) and don't make your OC solely responsible for everything that fans like about the existing character (don't make her the girl who got Mozart into music or the first person to ever suggest that Sherlock Holmes get into the detective business.)
If you want your character to date a main character you like, okay, but be careful. Remember a lot of fans out there want the same thing for their characters too.
Don't do Love at First Sight. It can happen in Real Life, but it's still thought of as discredited in fiction, and doing it for an original character will almost instantly get your character labeled as a Sue. Try to pace any relationship for realism.
Don't use Die for Our Ship to get rid of any existing love interests. That's another thing almost sure to mark your character as a Sue. If there is a confirmed love interest, just play it safe and leave her be.
Don't incorporate romance into your story if it would overwhelm an otherwise non-romance-centric plot. Unless the story centers on romance, it has to be worked in so that it is organic to the plot. Otherwise it's going to stick out like a sore thumb. This is bad even when only canon characters are involved. Shoving an OC in there just makes it worse.
Being related to a main character should be done carefully as well.
If your character is a child of a main character, it had had better be done in a way that makes sense. Being the child of two same sex characters just isn't going to cut it unless it involves surrogates or the setting allows that with some sort of Phlebotinum.
Being a long lost relative should also be plausible. If the main character is an orphan, you have plenty of opportunities. But even then don't just have the character pop up and announce the relation. What allowed this character to discover the main character? Why does it matter? Most people don't go around seeking out long-lost relatives, and even orphans don't always go looking for their surviving relatives.
If your character is the long-lost orphan child of a relative of one of the canon character, consider how they know that they're related. How did they find out? Why do they believe it? Also consider how the rest of the family feels/felt about the character's parent; this may well affect how they react to that person's child showing up out of the blue.
Also, you don't even have to bother with being a long lost relative if a main character is known to have a large family, or the series is legendary for having new relatives just drop in out of the blue. Just be one of the many cousins/cloned siblings/etc. that character is likely to have.
If a canon character is noted as being the last of his or her race/species, especially if this is a major plot point, don't introduce a previously-unheard of family member who is the real last one standing.
Don't have characters act differently around your character. Character Derailment is another discredited trope, so that also goes double for fanfiction. Characters should react to your character in a way that fits their personalities.
If a canon character has stated that they don't want children, don't have them suddenly change their mind and get pregnant/knock someone up just so you can introduce an OC in the form of their child.
If your original character is the child of an existing one, and the existing character is already at the top of their field (or worse, a grown-up child prodigy), your original character should never be better or more accomplished at what their parent does than they are. It's unlikely that your reader is going to find it cute that your made-up daughter of Sherlock Holmes is able to crack cases faster than him.
Spotlight-Stealing Squad is another no-no. Even Canon characters are often considered Sues for this (like Wolverine), and it goes double for fan fiction. The main characters are where the focus should be. Keep it on them as much as possible. That way, where there are scenes that need to focus on your character (the introduction of your character, any Character Development scenes), they will make sense.
If another character is The Chosen One, that character staysThe Chosen One. Your character doesn't become the new one instead (unless a story has that happen all the time, as in post-Slayerettes Buffy the Vampire Slayer). Now, if your character is chosen for something else, preferably a lot less significant than a main character, you could get away with that. Or your character could be destined to play Support Staff, like stopping a bullet or something like that.
Keep your character's age appropriate to what fits in the setting. If you are seven, and your character goes to Hogwarts, your character needs to be eleven at the youngest. Just think of it as you going to Hogwarts in four years.
Tragedy in the Back Story is common even for Canon characters. Just don't have your character's tragedies outweigh those of the main character - considering all the tragedies main characters go through, it shouldn't be THAT hard. And remember, if it's not going to play a part in the story, DON'T HAVE IT.
Pick one tragedy to befall your character in the past and build on that, instead of a mountain of travesty. If your character was orphaned at a young age, tormented by classmates, beaten and/or raped by a drunken foster father, then ran away from home and turned tricks to survive... at 12 years old, you are most definitely laying it on too thick. Any one of these can add the necessary angst without going overboard.
Whatever the tragedy, please be respectful to the real life victims and do the actual research first. Especially if your character has Rape as Backstory, since this is quite the Mary Sue cliche.
Similarly, if your character is still affected by her tragic backstory, make sure you properly demonstrate why she still hurts. Maybe it happened recently. Maybe it has something to do with the Power of Trust, which can last a long time. Maybe it's an old wound reopened recently. Maybe the small town/organization has a long memory and won't let the character forget. Having a character angst over small slights, imaginary persecution or things that happened long ago just makes the sorrow look cheap. Or maybe your Original Character just refuses to let the past go (especially if it was a big deal when it happened). But remember that if this is the case, this can be a serious mental issue in Real Life and should be an integral part of your character's personality.
And make sure that your character reacts in an appropriate manner to her tragic backstory, particularly in comparison to other characters; if your character has less reason to angst (either vocally or internally) than the other characters yet angsts more than they do, it won't make the reader feel more sorry for your character. Of course if it's your intention to make them out to be a whiny little bitch, that's fine.
If you want her to feel guilty, it should be for something she did, so there's a logical reason for her to feel guilty. Perhaps she was off playing around in the forest, rather than standing guard at her village when the Big Bad came and killed everyone. Maybe she insulted her parents just before her parents died. Angst can make a character compelling, but there'd better be a good reason for it.
Alternatively she may angst with a need for vengeance. This can make canon characters very cool and Bad Ass, but there's also the risk of making them whiny little bitches who just never shut up about all that vengeance they're going to have, turning angst into Wangst.
Avoid having the other characters excuse everything your character does solely because of her angsty backstory; just because a character has a traumatic Freudian Excuse doesn't mean that gives her a blank cheque to be a complete Jerk Ass to everyone around her, and the other characters shouldn't have to walk on eggshells around your character because of it. Some characters would not find it in their personalities to feel sorry for your character anyway.
Also avoid having other characters be attracted to your character precisely because of all the angsting and brooding she does. Contrary to what you may believe, self-obsession and self-pity are not attractive personality traits.
Don't have your character save an entire society; play it safe and leave that to the main characters (although as has been mentioned, your character can play support staff).
Choose your character's heritage carefully. Don't just choose a race because you think it would make your character beautiful, cute, or awesome. Choose one that you think would make your character fit in the setting best.
Redeeming the villain is not out of the question, but don't use Easy Evangelism or Redemption Equals Sex. Try to keep it within how it would fit in the story. Perhaps your character just incidentally, or accidentally, does the things that could help the villain when the other characters didn't in the canon story. Perhaps your character sees some good in the villain and makes it a mission to save him or her. Your character's arc could revolve around this idea, but make sure the villain's portrayal has grounding in the canon... and that a canon character didn't already do it. Luke saved Vader; your character doesn't need to do it again.
A Princess, or other kind of royalty, could work as an Original Character so long as such a position fits in the setting.
Similarly, if the other characters master an ability said to be very rarely mastered, don't let your character have this ability. Just... don't. It's easier that way. If she is trying to learn it, do not give her instant success. Rather, you may wish to show minimal success. Summoning, for example: let her pull an obedient canary out of thin air instead of some grand monster. Something like this can make for a good Chekhov's Gun later down the road. For example: Character is in a prison cell, the keys are in another room, she can just send the bird after them (but for your character's sake, do not abuse it and have this happen on the very next page). BUT, give her more failures then anything else (canary comes out with razor sharp talons, three heads, and a thirst for human blood) to show that she is far from perfectly skilled at it. You want her to master it? Save it for the sequel, if you get that far.
Your character screws something up; don't just wave it off (this doesn't mean mistakes the show treats as minor with the main characters). How your character reacts can be an important way to build your character. Does your character realize this was wrong? Is the character in denial? Does your character even care? But either way, the main characters should react as they would in the story. They should not easily forgive your character if they don't normally do that, unless they have a plot relevant reason for doing so. Tread carefully.
If you are having your character trying to atone (or angst over) a past misdeed in her life, make sure she has actually done something wrong. Having your character grieve over something minor or something that wasn't really her fault is cheap. Moreover, don't let other characters gloss over past actions with a pep talk to grant cheap resolution; your character must atone or get over her past through her own character development.
Phobias vary in their intensity, but they're still there. They don't vanish because somebody just forgot about them for a while. They don't vanish even when a character has to overcome them; most phobics are afraid for a long time afterwards. But they know they can do it now. Similarly, if the phobia never actually does anything - not even deepen your character - there's no point in you saying she's got a phobia of spiders when spiders will never show up in the story.
If you want to name a character after yourself, don't try to hide it; just do it. Be honest. Just make sure such a character has a minor role in the grand scheme of things, and that such a name will still fit in the setting.
In some fandoms, everybody has a Meaningful Name. In others, names are typically ordinary. In some settings, characters have very strange names, or their names are jokes. Sometimes it's a combination. As usual with such things, you should go with the flow.
There's no real need for a "Blind Idiot" Translation - Hanzi Smatter shows just how common this is. A character unwittingly named something like "Chronic Nasal Congestion" will immediately send you into Narm territory.
Use names involving gemstones, flowers, and colours with discretion (unless it's the norm for that universe).
If you want a name from any other language than your own default language, make sure the setting allows it... and that it's an actual name. People making up 'Japanese-sounding' names are the greatest offenders here; adding "-ko" to the end of a few vaguely Asian-sounding syllables is right out.
There is NO excuse for making up names in an existing language. If you think a foreign name will improve your character, you can find a genuine one on any number of baby name dictionaries on the Internet. There are even extensive lists of common foreign surnames and their meanings, so you don't need to make up those either.
Do not give your character a name with a 'creative' alternate spelling just to make her seem more special or unique. Jennifer is no less special or interesting than a Jynnifyr. This includes excessive punctuation, such as Jy'n'ff'er or J'yn-i-Ffer. It's much more likely to pull your readers out of your world and into one where they laugh or gag (depending on the reader) at your poor sense in naming*
An exception would be if it's your character's Embarrassing First Name due to parents thinking it would be a cute name, and your character prefers to use the proper spelling
If the character comes from a fictional culture where everyone's names are similarly made-up, you are also safe. If the character is an alien or otherwise nonhuman, a real name would be less realistic. If, however, the fiction culture has an established language or naming convention, follow the naming conventions rather than picking sounds at random.
You might want to dump it in a search engine before you use it, to verify whether it just happens to have a meaning. You can get some ugly coincidences.
Historically, almost every name at some point in its history was a Meaningful Name. In some cultures, this is still true; it's either given by hopeful parents, earned by one's own deeds or attributes, or indicates family status or place of origin. In other cases, instead of considering the meaning, a parent might name a child after another friend or relative, or just pick a name that sounds nice. If you're going to make a point of giving your character an unusual or meaningful name, think about who chose it, and why. Because seriously, nobody is going to name their child "dark blood" in any language unless they're either horrible parents or genuinely ignorant.
That said, be careful with overly fitting Meaningful Names. Parents cannot see into the future of their child, so if they call them Dragonslayer and the grown-up kid indeed ends up killing dragons for a living, it's plain unrealistic. It can be made more believable if there is a sound prospect that the name will be true one day, for example, said child is born into a warrior elite and the dragons are abound in the setting. On the contrary, an overly fitting surname will almost always stick out. Such things are better kept as a Character Name Alias or a nickname, but keep in mind that usually, nicknames are used only within a certain group, clique or subculture.
In general, don't do things just for your character that you aren't willing to do for the other characters. Don't slavishly describe only your character and leave everybody as a vague entity. Don't make up new words only to describe your character. Don't decide that your character's walk across the room warrants four paragraphs while another character's heroic rescue of somebody else gets a single sentence. Balance is everything, after all. Not all of your readers will like one character, nor will they all hate another. You want to give them all something they might find interesting.
With some experience it is simple to construct the Rolling Description - rather than a chunk of description, the character is described, feature by feature, gradually over multiple chapters. In the first chapter, she's just a young woman with auburn hair. In the second, you know she has green eyes. In the third, you find out she has long fingers. And so on.
No Purple Prose, unless the whole story is that. Getting most of the description is akin to stealing the spotlight. Your character should get descriptions no more detailed than the main characters'.
You can get fancy in your descriptions, like in moments that are important for character building, but only if the main characters also have fancy descriptions in such moments.
If it's a visual story, only make your character the focus when needed. Even if the story is told from the point of view of your character, the main character should still be "in frame" most of the time.
If your character still gets criticism, look at the kind it is. If it's insulting and not really getting at what the problem with the character is, and just a problem with you, it may be Trolling. If it's Constructive Criticism, you don't have to follow it, but at least consider their points.
The saying goes that every character must have a reason to be in a scene. Make sure your character has an actual reason to be there, rather than just because you want them to be.
Introduce your character to the story when it's necessary to do so, and make sure she doesn't disrupt the narrative. Your character should seamlessly work her way into the story without fanfare or attention - it's a well-written character that gets noticed, not a red-carpet introduction.
Don't introduce your character in the first sentence, especially in the manner of
"Hi, I'm [name], and I have [insert physical description]"
Also don't have your character look in a mirror just to "justify" sentences and sentences worth of physical description.
Don't spend entire paragraphs on describing your characters clothing unless that particular clothing is for some reason very important to the overall story or if the description of the clothing is meant to convey something about the character other than her fashion sense (ex: you might convey how a bride feels about her impending marriage by giving a detailed description of her wedding dress from her perspective.)