Undertale AUs are what-if changes to the universe of Undertale.
AU categories are used to differentiate AUs and to avoid confusion between AUs (categories are not AUs themselves).
An AU can fit under multiple categories.
The basic types of AUs.
Some or all of the canon Undertale characters swap roles and/or personalities with the other canon Undertale characters. e.g: Sans replaces Toriel. No new characters are added, and the story is relatively the same for the most part.
If only one character pairing is swapped, it doesn't fit in this type. In that case, the AU is most likely in the Character-centered type.
A mixture of a story, game, movie, TV show, or book, or personal characters and Undertale; A two unrelated universes/shows/etc combined into one AU.
Every single character in Undertale is changed while still remaining in the same basic story in some which way or form. AUs that only affect some of the characters are not found here. AUs that change only during the time Frisk is in the underground are not found in this category.
Some AU categories are part of this type:
As simple as it sounds, these are the AUs in which every character is the same person as every other character. Of cause this brings up questions like, is the Undyne in the Captain of the Guard role in Undynetale the same as canon Undyne or are they the Undynest Undyne in the multiverse (or an amalgamation of every other character, as she is "everyone"). We may never know.
These are comedic in nature and rarely make much sense beyond amusement value.
The species of all the characters have changed. Being changed into objects also works here.
AUs that are focused on a particular set of characters. These include headcanons, extensions, and flat out new ideas.
AUs in which 1 or more characters are replaced with real people.
The tone of AUs.
AUs that are mostly comedic in nature. Bare in mind that a Parody can be bother dark or comedic so they aren't necessarily the same thing.
A category for the 'Fell' version of other AUs (e.g. Swapfell if a fell iteration of Underswap.)
Warning: Some of these AUs contain themes that may be disturbing to some viewers.
AUs with the goal of creating something scary, insane, or disturbing. Some AUs that follow the genocide route are also found here, but not all are geno-route-only. Some possible themes include suicide, drug use, alcohol use, depression, death, gore, insanity, disfigurement, pain, etc.
It is suggested you read the short bios of these before googling them!
The time where the AU's plot happens.
AUs that cover the backstories of characters and lore or change the backstories, leaving most other things the same.
AUs that change the plot in the middle of the reset-able timeline (After the main story begins and before the endings).
The change affects most or all characters, otherwise it belongs in Character-centered.
- AUs in this category should be moved to the proper subcategories.
AUs that are sequels to the original Undertale or other AUs.
They are set after a route (Leaving the Underground/Destroying the world). Otherwise, it belongs in Special Event.
AUs that happen after the Pacifist Route.
AUs that happen after the Neutral Route.
AUs that happen after the Genocide Route.
Post-/Soulless Pacifist AUs go here.
The way the AU's story is told.
Stories told through animation series.
Stories told through comics or graphic novels.
A type of AU that has/will have a playable game/mod.
AUs written as text based series.
Miscellaneous AU Categories
Categories that don't fit in the above categories.
AUs made by large parts of the community as a whole, instead of by just one person. Everyone has a common idea. Which is why they are called 'Community AUs, Floweypot is a good example. There are no real creators until they are confirmed by the community.
AUs that are a combination of two other AUs or modifications to pre-existing AUs.
AUs that are made to be a parody of Undertale, other AUs and/or another piece of media.
AUs that were only created as a joke, with no intentions of becoming a serious AU.
The story does not take place within the Underground.
AUs in which OCs are added.