Go there to read the whole thing, and see the image and links. Here I merely repeat the core of the document, which he emphasizes were rules told to him, not that he made up. The words below are his:
[Here are] required steps for properly representing a feminist heroine in movies and TV … It makes a lot of things very clear to me. Including how otherwise talented writers are so consistently ruined by these rules.
First. The patriarchy is real and must be treated as such. The female protagonist is oppressed by it. This is not optional.
Second. She is already the key to a better world. She has all the skills she’ll need, inherently. She’s the Avatar, you just got to deal with it!
Third. Her biggest challenge isn’t defeating the antagonist, it’s defeating disbelief in her. Men, in particular, won’t believe she’s as amazing as she really is.
Fourth: She is better than any male mentor figure. There is nothing that she can be taught by a man regardless of his age, experience, or expertise. The guidance he gives is just another example of mansplaining and must be shot down hard by her. If there is a male mentor then he is the first man that must be defeated.
Fifth: She enters a new world that forces her to prove herself.
Sixth: She escapes the patriarchy. She now breaks the chains that held her back. Usually by confronting her true male oppressor.
Seventh: She is briefly overwhelmed but then bounces back. This is where she levels up her already enormous power.
Eighth: She defeats her male oppressor.
Ninth: She is now an independent woman who will never need a man. And she must continue her journey alone. Any other person in her life will hold her back. She will never love or be a wife or a mother. Those things would all hold her back.
Tenth: Realized self-actualization. She was always a goddess and just needed to believe how awesomely amazing she always was herself.
This list of requirements seems to fit every single one of the Mary Sues that have ruined every franchise.