Ah, I actually found the trope, and it seems you're missing the point.
The common thread between a Mary Sue and an Anti-Sue is that they're both the center of the universe; the plot and all the characters will go far out of their way for the sake of the Sue. Basically, if a trait or event...
That story is still up on RR. https://www.royalroad.com/fiction/91872/the-villains-cheat-code-when-a-gamer-becomes-the
Don't know if it's the one requested, or why it got 404d though.