Nightmare Moon returns and is hit once again with the Elements of Harmony rendering her a mischievous little filly.
Much to Nightmare Moon’s annoyance, Anon thinks she's cute as all hell and is the only one willing to put up with her antics and evil, so Celestia tasks him with reforming the bundle of misery and mischief.

Cover Image is by EvetsSteve, may he rest in peace.
Chapters 1-21 were converted into prose from my greentext stories with the help of Nav/WhatMustIDo

A human stays among ponies, mystifying them with his odd traditions and customs. It will be five years before Celestia and Twilight can send him back to his homeworld. Until then, Twilight wants to study him and have him experience pony culture. These are their stories.

A human has arrived in Ponyville that the Apples dubbed, "Anonymous."
Twilight is worried he might be dangerous. They know nothing about him after all. However, the Apples still treat him like a common pet, until he begins mimicking speech.