Out of all the clichés I have gone over so far, most of them were overly popularized tropes that could be fixed with some good old creativity to break each trend. You can attack the cliché of the modern interpretation of the vampire, a brooding loner who despite being a jerk always gets the girl, by combining the elements that made creatures like Dracula originally work as well as some of the stronger new elements added over a century later. Time travel stories can avoid being contradictory by having an easy to understand set of rules and keeping multiple universes out of the equation. The Skyler Perspective, limiting your creativity by keeping the story's focus on one character, can be vanquished by having three or more main protagonists be the star of the show. Almost all of these clichés have had some type of easy to spot self destruct button for potential writers. However, there are the rare few out there that no matter what have no second route to take if you step into their quicksand. Nothing can really be done to reverse these tropes once they are said and done. One such cliché that fills this criteria is one I am sure most of you have heard about somewhere in the past, the Gary or Mary Sue.
Gary Sues and Mary Sues are characters who are as bland as they come, with nothing making them stand out from the crowd of existing popular culture characters. Their hair in the worst cases are an unnecessary rainbow hue with unusual violet color eyes. Male or female, these characters exist solely to just move the plot along. There are no relatable characteristics that draws the audience towards this character, making them as replaceable as a cardboard cutout. They are completely overpowered with their abilities, and take away the spotlight from more deserving characters. Most of the time, Gary or Mary Sues are simply a bland version of the author put into a story. They are the stereotypical hero of most fantasy stories that almost anyone finds boring. If your character has reached this standard, trash them immediately. If you do not do that, your character could be the death sentence of the entire storyline.
Most people point to Bella Swan from Twilight to be the prime example of the always female Mary Sue. After all, she has no definable traits except for her clumsiness, was admitted by Stephanie Meyer, the author of the book series, to be a representation of herself, and somehow saves the day in every dire situation despite not even lifting a finger to fight. In my opinion though, Bella is a hybrid of the Mary Sue trope as well as something way worse; copying Elena Gilbert's characterization from the book series The Vampire Diaries, which came out over a decade before Twilight's 2006 release. A true Mary Sue in my mind would be a simple feminism symbol like Katniss Everdeen from The Hunger Games book series, an overpowered character like the anime version of Maka from Soul Eater, or the creepy wish fulfillment character of Anastasia from the Fifty Shades of Grey book series. They are true Mary Sues, unlike the copy and paste Bella Swan.
As for the Gray Sue, there is no better figure for this position than the DC comics character Superman. Despite the character's backstory being well thought out, what is Superman at the end of the day besides a symbol of the potential heroism we contain inside us all? His powers until recently were too overpowered, with seemingly no limit to what he could do to defeat an enemy. It took his death at the hands of Doomsday and limiting his abilities to only work at the presence of the sun to control this major issue with the character. There is a reason some people really love the movie Man of Steel, which divided audiences completely in half. It humanized Superman more than any previous incarnation, putting some realism into the good and bad consequences of his existence as a bringer of justice. Love it or hate it (I personally prefer the older movies) Man of Steel was somewhat of a step up from the Gary Sue characterization we were presented with before.
Looking at all of these examples, a pattern should be starting to emerge. Each character has a trait that defines them as either a Mary Sue or a Gary Sue. For a character such as Katniss Everdeen, it was feminism just for the heck of it. For a character like Superman, it was being overpowered. Any character of this type normally ruins the quality of a story, as well as actual investment. If you have a character that fits any of these molds, get rid of them immediately. They will poison your story to the point of making all of your hard work writing an epic fantasy tale fruitless.