Your character can leap tall buildings in a single bound.
Your character has a pet lion.
Your character can read minds (in a world where this is not a common ability).
Your character has long violet hair that looks blue where the sun strikes it.
Many main characters have unusual traits, skills or accessories like this, and some of my favorite fictional people have several. Take Sherlock Holmes, for instance. He’s a brilliant detective and a master of disguise who also does chemical experiments and plays the violin when he isn’t writing monographs. He's also real, intriguing and just plain fun to read about.
On the other hand, when I tried to critique a story featuring a hero with several such qualities, I didn’t find him as interesting. I wondered why this character didn’t work for me. Barra, Matthew Woodring Stover’s heroine in Iron Dawn, has several Cool Factors – she’s an axe-wielding mercenary with acrobatic skills, a mystic power and a wolf for a pet. She speaks six or seven languages and men find her very attractive despite her scars. Oh, and she’s also a princess. So how does she not set off Mary Sue alerts?
1. The character comes first.
Readers are more likely to identify with and sympathize with a character if the character’s unique traits aren’t pushed at them too quickly. Iron Dawn doesn’t begin with Barra chopping her enemies in half with her broadaxe; it starts with her writing a letter to her children back home, to let them know she’s sending them a few gifts. The gifts are actually the last valuables she owns, since she’s broke, but she doesn’t tell them that. I was intrigued and sympathetic, and if I care about a character, I’ll keep reading.
2. The cool skills and accessories are introduced gradually.
New writers sometimes think that the shiny facets are what’s most interesting, so they flash these in the reader’s face early, sometimes stopping the action to describe why the character is unique. Unfortunately this can make the character come across as a collection of special powers and special weapons, rather than as a person. If the character is a meal, the cool skills are glasses of wine. Drinking three or four glasses in quick succession will leave me dizzy and wanting to lie down, but spacing the glasses out through the meal is much more enjoyable.
This doesn’t apply to very minor characters. If a magician is only going to make two or three brief appearances in the story, describing him as "the man with a covered mirror and a price-list of spells" would work better than trying to develop him as a character.
3. The traits are made plausible.
In fantasy, it's often easier to believe the impossible than the improbable. If the story begins with the heroine having a magic sword, I'll accept that at face value and hope that the sword is an interesting one. But if the author mentions at the start of the story that the heroine was raised by bottlenose dolphins and speaks their language perfectly, this will have to be convincing and plausible before I can believe in her struggle to rally the local dolphin pods against the local pirates.
4. The character has significant flaws
I was shocked when I first read about Sherlock Holmes injecting himself with cocaine. Most authors won’t (and shouldn’t) go this far, but it’s great when characters have flaws which balance out their virtues. Scarlett O’Hara’s unscrupulous nature, Bigwig’s aggression, Jaime Lannister’s incestuous obsession with his sister… positives are good, but carefully chosen negatives humanize characters, round them off and lift them above the common herd of heroes. This was a problem with the story I critiqued – the hero didn’t have any serious flaws or weaknesses, so he came off as an author’s darling rather than as a powerful, three-dimensional personality.
5. The antagonists have their own special powers and intriguing traits
Holmes has Moriarty, Bigwig has Woundwort and Barra has God himself. Yes, you read that right. If the antagonists aren’t as souped up as the heroes, the story may not be too much fun – in fact, the heroes might even come off as bullies for picking on people who are evidently weaker than they are. Give them all bright facets – just not too many each – and then watch them strike even brighter sparks off each other.