info about how the multiverse works
the void:
the void is a dark connection that holds the multiverse together like a string, surrounding and keeping all aus and each of the respected countparts held in nearby connection.
the aus do move around the vast space but the connection is never dropped (similar to outerspace and the solar systems)
however, unlike what many believe, the darkness of the void itself isn't the dangerous part (aside from the darkness slowly driving anyone who lives there mad). the void is its own source of power, this power often breaks and shatters those caught within it, as no living entity should be able to withstand the pressure.
however, there are acceptions, whether that be the au that the void belongs to, or the general area of the void surrounding the au, on the occassions where it is altered, the void becomes less dense, often letting those trapped within it survive or even gaining the power of the void.
there are shallow points around aus where they can be observed from the void and times broken through, however this is more of a rare occurrence than something to be concerned about.
the antivoid:
the antivoid is a massive web of connections and chains that travel through the void, giving a safe space for beings of all types to travel and interact in, there is little to no checkpoints nor landmarks in the antivoid, seperating from the general areas is dangerous and would likely result in others going missing.
however, just like the void, the antivoid is not that safe either, aside from the ability to become glitched if present for to long (error and errorberry as examples) there is also madness that can settle in.
this is due to the fact that, aside from nothing being there, you cannot get hurt, hungry, thirsty, tired, rested and may become generally unaware of your surroundings in the bright light of the antivoid. (along with the fact that you cannot properly die while in the antivoid)
(nightmare's castle, the antivoid town and errors stings are all landmarks that the creatures of the antivoid use to travel safely)
if you were to die in the antivoid, from a fight or anything else that has the capability to kill you, you will be returned to your universe (aside from the classics who would be permanent death and erasure of that character) however, for a period of time you will have no memory of the antivoid, the multiverse or anything to do with even being an au yourself until a timer runs out, once that timer has ran out then all memories will be returned and the au is reopened to the multiverse.
if multiple characters have left a universe and one of them dies, all characters from said universe will be sent back with all their memories erased until the timer is up. (for example, underswap sans and underswap papyrus are in the antivoid, and underswap sans dusts in a fight against the bad sanses, he and underswap papyrus will both return to underswap with no memory of anything that happened, and in doing so will also reset the au back to the beginning of the timeline, the main character will have no memory of this happening (frisk, chara, aliza, etc depending the au)
one of the most interesting facts of the antivoid, is the fact that even if a character cannot remember the resets of their world, will often remember things that happen in the antivoid or other aus that they don't belong to;
for example, one of the versions of underswap sans has no capability to remember the resets from underswap, however, if he talks to dream sans and ink sans, he will remember that conversation, though unfortunatly, even if he mentions the current reset, he will be unaware that a reset has occurred unless he brings it up again to the others of the multiverse (often leading him to repeating himself if many resets occur in short bursts)
for the issue that may arise with them remembering the multiverse conversations, it often feels like deja vu instead, along with the fact that if a conversation was started in their world and continued through a antivoid gateway (or portal, personal preference of naming), they will only remember the antivoid half.
it also often doesn't click until its brought up that a reset has happened, similar to doing something but forgetting it till you see a photo of sorts, even with the memory there in mind.
The antivoid is also not a technically infinite space, it's just relatively large tunnels connecting the aus, often times being thought of as just a large open space. The location of each landmark previously stated, shifts and changes as the antivoid tunnels move around, however they will always be nearby to the au thar they were created near to, unless it's specified otherwise.
aus:
the aus themselves are attached by small tunnels from the antivoid that are blocked off with a universal wall, on rare occassions these may crack open and let characters slip through unseen or unheard, often times getting lost within the antivoid.
the universal orbs that the aus inhabit are constantly moving and bouncing around eachother, if they are close enough to set a temporary connection between two universes, there are often glimces into that other world (often known as douples, as no one is often aware of the aus that are around).
the walls for each au have a few ways to be broken through:
as mentioned previously, gates/portals that outcodes and powerful beings can make (ink, error, dream, nightmare, fresh, etc)
they can tear randomly into either the void or antivoid (this is more of a rare occurrance)
or can be broken open with force from inside the universe (most of the time how gaster or anyone in his place get into the void)
aus themselves can be of anything, whether a slightly altered timeline of events or design (like toriel with a different dress, or alphys wearing a different labcoat) to massive changes to the story or characters (like underswap, any of the aus with humans instead of monsters or even ones destroyed)
there are also aus that are blocked off or locked down, often having no way to enter or exit the general area.
doodlesphere (headcanon):
(This part is canon) with the doodlesphere, it's the unknown place that store all the au pages, only a few characters are able to get there, it's the home of ink as he goes there to refuel his vials so he doesn't end up becoming a husk or a lifeless skeleton on the ground.
(Headcanon time) the doodlesphere itself is a large reality that's not connected to the antivoid in the traditional sense, having no antivoid pathways to make it easy to get into, ink had managed to stumble into it by pure chance with the help of Broomie, being kne of the few characters to be able to open a gap into the doodlesphere.
Due to there being no pathways or connection areas, it's one of the most difficult locations of the multiverse to access, as it almost constantly moves around unless it's been stalled by bumping into another au orb, howrver there's nothing that it can do as it's not a location that has inhabitants.
classic universe:
The classic universe, a unique location of the multiverse, being the main source of all the characters and locations for most aus, however in being that, they are one of the most important locations of the entire multiverse.
If a character feom the classic universe dies feom unknown sources (something within the multiverse) then it is almost impossible to bring them back, as it completely erases the character from the multiverse.
The only time they would be brought back is a full multiversal reset, setting everyrhing in the multiverse, including aus and the void, back to the beginning of the timeline.
The classic universe itself is unique in that there are multiple versions of it, but they aren't classed as aus. As everyone has their own different way of writing the classic universe, unless large changes happen then it becomes a timeline au, like geno sans.
The classic world is also not the true original, as that would be the prime universe, the original game of undertale, but the classic is a version that is accessible to the rest of the multiverse.
Being the classic universe there are a few things that it has to follow unlike other aus where this isn't as important.
1, a character cannot be gone from the universe for to long without a replacement.
This means that if someone, like classic sans, decides to go into the multiverse for whatever reason he wants for longer than a day, he needs another sans to take his place, now, tgis isn't to important with having to hide the multiverse, it doesn't have to be exact copies, even someone like nightmare or error could take sanses place, it just needs to be an entity that looks like sans.
However, if the classic world doesn't know of the multiverse, then it requires a more sneaky approach, having sanses that look mostly the same to take the place of classic.
of course this can be dangerous but often times it doesn't change much, as long as the correct au is put in place.
When a reset happens in the classic universe and it's not classic sans, nothing much will happen to the sans, they will be reverted back to how they normally look, and would have to change or contact someone about getting items that allow them to look like classic again.
However, if the human/player decides to genocide the underground, as soon as the sans is killed, they are returned back to their universe, which then causes a few issues with trying to find someone to replace the sans as they themself will not be aware they just died.
2, there can be multiples of a character in the classic world, there isn't to much issue as it doesn't track the amount of those in the classic, however it is still rather dangerous as it may cause confusion of a glitch in reality when the reset occurs, as there isn't supposed to be more than 1.
Multiversal aus
Just like normal aus of the classic world, there are also multiversal aus, more along the lines of different galaxies and dimensions, the multiversal aus are some of the most difficult things to get to unless you are from that universe, occassionally there are rifts between the multiverses that allow for travel between them, but often they are blocked off from the rest of the multiversal areas.
Unlike the aus, multiverse aus are rather chaotic and often times broken, not following the normal rules of what is known by other universes.
