Criterias:

- At first, Nightmare Moon must not have her own body and relied on a host.

- Nightmare Moon must possessed only Celestia, Luna, and Twilight

- Nightmare Moon must not thought to herself as "I'm gonna do evil just because I'm an evil villian" or something two dimensional like that.

- The story must not totally revolved around Nightmare Moon having mental sex with the host.

Optional but encouraged:

- Nightmare Moon is manipulative

-Nightmare Moon is weaken and must relied on the help of the host to do stuffs

- story was set after the return of Nightmare Moon(not ancient Equestria)

Examples
https://www.fimfiction.net/story/10149/entwined
https://www.fimfiction.net/story/448810/twilights-nightmare

Twilight is the culmination of a thousand year plan to revive Nightmare Moon.
After her defeat, in a weakened state, Nightmare Moon lies dormant within Twilight’s subconscious until lesson zero occurs.
Empowered by Twilight’s fractured sanity and now capable of controlling her new host, Nightmare begins a new plan, one that Celestia and Luna themselves would never imagine.
Living a quiet and peaceful life away from politics and rule.
she might just get it, if she can juggle her friendship lessons, the weekly monster attacks, and a growing cult of Nightmare followers that keep trying to convince her that she deserves the crown.
All while trying to piece together the broken mind of her host.

7875749
Is that a real story or...?

nope, i just like coming up with story concepts. i misunderstood what the post and thought you were asking for story ideas. i only recently found out you were looking for stories.