Hey guys, this is perhaps my first help Blog for this year and today, we are going to talk about Mary Sues, and why you should avoid them. While not a stranger to 'profesional works' it is a terms most commonly associated with Fan Fiction.
First things first what is a Mary Sue. A Mary Sue (Gary Sue for guys specifically, but Mary is the overall term) is a strawman term (it's used to represent a group, an issue or a problem as a concept and not an individual(s)) and it refers to when a writer creates a character represents themselves. Mary Sues are less characters and more fantasy trips, in often cases power trips.
Now, this isn't a problem in and off itself. One of my favorite characters Rung from the IDW Transformers characters is quite possibly a Mary Sue of writer James Roberts. The issue arises from how people know when to call a character a Mary Sue, because a Mary Sue is synonimous with bad characterization
The main issue with this type of character, the reason people call foul, is bad, or the simply lack of, characterization. A character is less of a character and more a vehicle for the reader to put themselves in. Which in some cases isn't a bad thing, but in most cases it wreaks of lazy writing.
Mary Sues are accused of being power trips, going through the story with no real issue or no problem they can't solve with ease. In a franchise like Ultraman, a Mary Sue would often get ridiculously powerful power ups because. They don't feel earned and it feel like other characters are getting cheated.
A fine example is Ginrai from Transformers Masterforce. Ginrai wasn't there at the beginning but upon becoming a Godmaster (don't ask) and joining the Autobots...he was made leader of the team...because he was the strongest. Never mind that Metalhawk was originallt the leader, was centuries old compared to this human (or cyborg, whatever). Then he got an Upgrade and another and he only lost once if my memory is correct, and then he got an upgrade.
Then look at Star Saber a guy who appeared in the next series Victory, who I think was intended to be the next coming of Optimus Prime. He was powerful, yes, able to be beat most of the villains by himself, even as teams or combiners, but he was defeated several times, had to fight once while sick from a prior fight and it was made clear that he had to rely more on his skills rather than brute force to defeat his enemies. He was also a leader because he had served centuries as a field commander and he had a characterization similar to Prime, yet was different enough.
He could be called a Writer's Pet, which is not as bad as a Mary Sue, but teeter on the edge of being one. Though in all honest, I like Star Saber.
A mary sue can be more than just a main character, they could even be a side character. They could also be more subtle than the examples above. Imagine two people having an arguement, a series debate that resulted in a deep history together, or over a controversial topic, and yet a character can just walk up to them, calmly talk to them and solve the issue. Now that doesn't automatically make them a Mary Sue, they could just be very wise. Do remember, 'conflict' in wirting isn't just fighting, it's also drama, problems mundane or fantastical that must be overcome.
Why should these kind of characters be avoided, well for the reason they became a 'thing', the reason why the term appeared in the first place. It's bad writing. Granted you could make a character who is made to represent you and not have them be a Maru Sue and you can have a character not meant to represent you, but be a Writer's pet or worse.
You avoid them because, they clearly are not a challenge to write but also not worth reading/watching.