>>37771554An actual Mary Sue refers to a character that is (typically) a self-insert, has an unprecedented level or type of power for no apparent reason and is generally assumed to be innocent and liked by everyone.
These are bad because they are indicative of the writer being focused more on simply showing how super special their character is rather than writing a story, and as such the writing surrounding those characters can often be contrived and unfocused.
Any other use of the term Mary Sue is misuse of the word and I can't speak for it. Unfortunately, people misuse words over time, slowly increasing the vagueness of their meaning to the general public.
Also theoretically a Mary Sue isn't even an inherently bad character, but there needs to be a specific context for it to work. Isekai Smartphone's MC is absolutely a Mary Sue, but his character being overpowered to the point of ridiculousness and girls falling all over him is literally the point of the show, something it makes clear from the start, it's a fantasy fulfillment show about a dude who has god mode on.
