So You Want To Have A Powerful Or Talented Character Who Probably Won't Be Perceived As A Mary Sue?
Many, many, many times I've seen people complain that they can't write or play powerful characters without these characters being labelled as Mary Sues. I really have only one thing to say to this: it's probably either because your characters are Mary Sues, or because you're presenting your character the wrong way. Sure it's not the former? Okay, then let's get on to how you can present your character so people probably won't grab the torches and pitchforks. This article is largely intended for fan characters, though most of it applies to other character types as well. Start by describing what makes your character tick, not what makes xir special. When you begin your character profile/pitch, leave out your character's appearances, superpowers, and canon connections as long as you possibly can. If you have a well-developed character, you should be able to describe xir without mentioning xir powers, abilities, or canon connections quite easily. Remove irrelevant specialness.
Related: Sci-fi and/or Fantasy Writing tips