As has been alluded to in previous sections, The Character and Relationship Tags will Synn any AU disambiguating tags that are entered into them, synning them under their Canon-Compliant variations.
This means that, if you want to search for "Underfell Sans/Reader" fics, and you do so using a search in the Relationships Tags, you will end up getting results for all Sans/Reader fics. This makes finding AU content you want seemingly impossible.
The solution is to use Additional Tags.
UTMV AU Tags are already canonized as Additional Tags, both as Character Disambiguating Tags and as Relationship Disambiguating Tags.
This features allows the Event to calculate metrics for UTMV Ships and determine which of them are Rarepairs.
How to Tag a Whole Alternate Universe
When a fic takes place in a specific kind of Alternate Universe, or involves multiple characters from the same Alternate Universe, you may find you want to add an AU Tag in the Additional Tags entry field using the Full and Proper Name of the AU in question with the pre-established AU format.
Examples:
Alternate Universe - [AU Name] (Fandom)
Alternate Universe - Underfell (Undertale)
Alternate Universe - Dancetale (Undertale)
This is used to broadly search/filter the AU itself. Other, broader kinds of alternate universes (such as Victorian Era, Vampires, and 1920s) are also used with this syntax, sans (heh) the Fandom tag, but for the purposes of this Event, those Broader categories won't be factored in to determine Rarepairs. The event will only recognize Fandom-Specific AUs, which are disambiguated with a Fandom designator (as used in the Undertale/UTMV fandom) or which have a Fandom-Specific Term in the name of the AU itself (making the need for a fandom designator redundant in that particular fandom).
Tagging the AU itself is not required for a work to be a valid entry, but knowing and understanding what the "Full and Proper Name of the AU" is for the next sections to make sense.
The Event will recognized any AU tag which has been canonized and wrangled already. In the event of any disputes over naming conventions, the Event will defer first to pre-established AO3 tags, and second to any primary sources which can be found from the original creator of the respective AU(s).
Additional Tags: Character Disambiguating Tags
If an AU Character is involved, it is recommended to add a Character-Disambiguating Freeform Tag in the Additional Tags Entry Field. A Character-Disambiguating Freeform Tag is a Freeform Tag that specifies a distinction for a particular AU variation (or a distinct and named Original Character) in place of a true Character Tag.
AU Character Disambiguating Freeform Tags are considered by the Event to be child-tags of the Canonical Character True Character Tag. To qualify for Bonus Tickets, a Work must tag the parent Character Tag along with the Character-Disambiguating Freeform Tag.
Multiverse Disambiguation Policy
In the same vein, MAUs (such as but not limited to: Underverse) are also not considered as distinctively relevant, as the characters which comprise them do not have any disambiguating features to make them different from their non-MAU counterparts for the purposes of shipping.
To put it another way: it would not make sense to disambiguate "Underverse Underfell Sans" from "Underfell Sans", or "Leviathantale Reapertale Sans" from "Reapertale Sans", in such a way as to make the ships they are a part of unique to each other, and therefore they will be synonymous for the purposes of this Event.
Rarepairs WITHIN those continuities are still eligible (such as if Underverse Red/Lust is the focus, or Leviathantale Papyrus/Nightmare), but the continuities themselves do not inform upon that judgment. (Underverse Classic/Red isn't distinctive from Non-Underverse Classic/Red to make it relevant as a taggable rarepair).
Obscure AUs & Original Characters Policy
Personal and Less Well Known AUs are perfectly valid, so long as they feature 3 or more Canon Character derivatives. AU types which do not feature at least 3 will be considered OCs for the purposes of this Event, whether or not their correct and proper tagging would designate them as such.
Example: While Ink is to be tagged by his name using his Character-Disambiguating Freeform Tag, he is for the purposes of this Event designated as an OC.
As OCs, they will be categorized for the Purposes of this Event as being a Child-Tag of the "Original Character" tag, and by extension ships involving them will be considered Child-Tags of "[character]/Original Character" Tag.
This year, OCs will be considered on a case-by-case basis. However, any OC which already has a Canonical Character-Disambiguating Freeform Tag will automatically qualify. Pioneering an OC's Character Disambiguating Freeform Tag is outside the scope of the Event's intended purpose, but we're being kinda lax this year.