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.

AU Types

The basic types of AUs.

Switch Up

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.

Basic Change

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.

Concept Change

AUs that change the basis of the story, such as sequels and backstories.


AUs that are focused on a particular set of characters. These include headcanons, extensions, and flat out new ideas.


AUs in which the characters are replaced with real people.

AU Tones

The tone of AUs.


AUs that, as opposed to Comedic AUs, actually hold a serious story and such. Just because an AU has a serious tone does not mean that it must be serious all the time, just most of the time.


AUs that are mostly comedic in nature. Bear in mind that a Parody can be either dark or comedic so Parodies and Comedic AUs aren't necessarily the same thing. Nevertheless, they can also be both.


AUs that feature horrible, evil, and/or murderous Monsters.


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. Horror can also include Terror, and effects on psychology. This could include things like dystopias and the like.

It is suggested you read the short bios of these before googling them!

AU Continuities

The time where the AU's plot happens. All of these are sub-types of Concept Change.


AUs that cover the backstories of characters and lore or change the backstories, leaving most other things the same.

Special Event

AUs that change the plot before or in the middle of the reset-able timeline (Any time 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.

Written story

AUs written as text based series.

Miscellaneous AU Categories

Categories that don't fit in the above categories.

Community Shared

AUs that are updated by the community as a whole, rather than by just one person. Everyone has a common idea, which is why they are called 'Community AUs'.

AUs of AUs

AUs that are modifications to pre-existing AUs.


AUs that are made to be a parody of Undertale, other AUs and/or another piece of media.

Joke AUs

AUs that were only created as a joke, with no intentions of becoming a serious AU.

Outside the Underground

The story does not, within its entire story, take place within the Underground, but does take place within a Universe. Only applies to AUs that occur during the resetable timeline.

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