It's never over

OCs

I don't care if my OC is a Mary Sue.

Yeah, she's Harry Potter' sister. Yes, she looks like Lily with James's eyes. No, she is not the 'Girl Who Lived.'

Just because several people made stories like that, with Harry's twin sister looking like Lily and being the Girl Who Lived, doesn't mean they all are like that.

Another common story; Sirius Black's daughter.

Okay, yes, that would be fun to write about. Yes, it's crazy over used. No, I don't think you should stop writing your story because people tell you it's Mary Sue, cliché, whatever

There's also Remus Lupin love stories, which are perfectly fine, Marauders Era Sirius Black love stories, a whole lot of Draco Malfoy love stories, any member of the Weasley Family love stories, ANY CANON CHARACTER LOVE STORY
Yes. They are cliché. Overused. Written too many times.

But writing fanfiction is about fun.
You should be writing this only for yourself.
Who cares if you're a 900 year old time lord who looks sixteen and goes to Hogwarts to save Harry Potter and falls in love with a canon character

I don't.

You shouldn't. (I'm not trying to tell you what to do, just a suggestion.)

People who matter don't.

So continue to write the most cliché fanfics ever. Maybe, if you finish them, you'll find plot twists that don't make them as cliché.