Undertale: Our Story is an AU with a Post-Pacifist sequel, where Frisk returns to Underground and discovers several changes there. The AU is still in the process of creation.
More options woulds be added during the battles, like new buttons and new enemies. The "Mercy" could not be left out, but some enemies would have to be killed.
- The Ruins: Originally, this location would be old and almost uninhabitable, with the difference of the presence of different (and more) monsters.
- Snowdin: A very cold and quite inhabited place in the Underground. It has a noble and diverse population, as well as many more areas with Puzzles.
- Waterfall: In addition to the presence of other monsters and more residences in the place, one does not notice many changes.
- Hotland/Core: Both gained a more technological appearance and is more apt to be inhabited.
In Mount Ebbot, after a pacifista route, Flowey gets enough power from the human souls to become Asriel (God of hyperdeath form), taking the place of the new king of the underground. Then, with his powers, Asriel create multiple monsters souls, creating as soon a "new generation" of monsters (Like Pokémon games, which change pokemons every generation).
Meanwhile, in the surface, Frisk and all the monsters are living in peace and harmony with the Humans. One day, Alphys asks Frisk's help to make the new body of Mettaton (Mettaton Alpha) for his new show, so she says they needs a Tool left in his old laboratory, in underground.
After this, Frisk go back again back again to the mount ebbot/underground, to fetch the tool and discovering all that new monster empire.