Mary-Sue - The Ultimate Guide

A character's name

Let's face it, we're not the most creative when it comes to names. We'll end up giving our characters rather common names, like Crystal, Poppy, that sort of stuff. Sometimes we can't even decide on a name for our character, and will hesitate on creating this character until we pick a name.
But that's where the first Mary-Sue trait comes in. We will sometimes give in, and use multiple names for our characters. It's okay if it's two names, though. One could be their first name, and the other as their middle name, then put in a surname. Heck, people can even have 2 middle names.
My point is, if real people in the real world have the amount, it's okay for your character.
So what makes it a Mary-Sue trait?
Well...
It's people who give their characters WAY too many names.
For an example, let's play a game called "What's Acceptable?"

Here are two OC names. All you have to do is spot which is the Mary-Sue.

Penelope Rizzol
Diamond Amethyst Sapphire Ruby Topaz (Diamond for short)

Yeaaah, it's pretty obvious which is the Mary-Sue. If you have a lot of names and then you just put ___ for short, chances are it's a Mary-Sue.
Unless it's a case that makes sense.
For example, I once wanted to make a character for the Sonic fandom, who would have had the name "Toni-Anne Marie Mitchell". Toni-Anne was her full first name, but she would've preferred to be called Toni. Marie was her middle name, and Mitchell was her surname. Cases like this do NOT make your character a Mary-Sue, as there are people in real life who have a first name like that, and would prefer to shorten it.

If you wanted to make another character related to your first one, you could use a middle name from your first character, since sometimes parents give their children a middle name that someone in their family is or was called. So, say you had a character named Amber, and she has a twin sister named Ember. Amber gave birth to a girl, and decided her daughter's middle name would be Ember, like her aunt. This is completely fine, as this is what families do in real life. Not to mention it's cute!