A Class:

Desolate universes containing only one thing or a small collection of things (an asteroid, star, star system, etc) with nothing but void everywhere else if only ranked A. (Nothing bigger than a galaxy.)
Some universes may briefly become this class near the end of their lifespan, making this class very commonly paired with N and D class.

B Class:

Universes filled with nothing but, or a lot of the same thing, sometimes floating alone in space (Nothing bigger than a galaxy.) Some of these universes can repeat areas over and over, making them very confusing to traverse.
This class, thanks to how similar it is to A class, is very commonly paired with it.

C Class:

Universes that have fused with other universes. (Not to be confused with Q class, where the universes are linked in a way but still separate places.)
This class, while common and naturally occurring in D and N class universes, also occurs unnaturally during the events of the series at a rapidly increasing rate thanks to an unknown force.
Populated universes that have fused together often do so very violently, causing fatal results for those living in it. If the residents of a fusing universe aren’t killed immediately, the change in the reality’s rules can still have devastating and fatal effects on them later.
For mimic universes, the fusion cause damage to the viteroite nucleus/nuclei and result in painful psychological consequences or even death.

D Class:

Dark era universes. These universes are typically found on the outer edges of the multiverse, fading into Akyliss. They have little to nothing in them, and are sometimes completely empty.
M.U.E.C.I.F positions devices in these universes that send a repeating signal back to their headquarters. They track the rate at which these devices stop sending back signals to determine both how fast the multiverse is expanding, as well as how fast universes are fading out of existence. Thanks to their research, it’s very clear that the multiverse grows at a pace faster than it’s edges fade.
Because of the nihilgenesis, these universes are created unnaturally all throughout the multiverse during the course of the main plot.

E Class:

Universes with mysterious “man made” structures. They can be abundant, sparse, or even just a single structure. In some extreme cases, the universe can entirely comprise of one of these, or a fusion of several.
The rules of these universes allow the structures to last much longer than they normally would, and any damage done to them is silently repaired by natural forces over the course of hundreds of years. These formations have priority over anything else, and often outlast everything else in the universe- some even lasting until their protons decay (if applicable to the universe) or even akyliss.
Structures in these universes are formed alongside the universe, and created by ???’s memories. They’re often misremembered, causing a majority of the structures to be surreal or nonsensical. Despite what one might think, there is no link between E class universes and P class universes, and the two classes don’t overlap any more than any other class. E class universes instead heavily overlap with J class.
M.U.E.C.I.F frequently sends out notices to their interns that the structures in theses universes are odd, but ultimately a normal part of the multiverse and shouldn’t be reported as anomalies. These notices are often in vain.

F Class:

A classification that doubles as a warning. M.U.E.C.I.F enforces this class when they identify a major anomaly that’s consistently in the universe and could potentially cause issues. When put in place, they will urge people to either be cautious in the universe, or avoid it entirely- sometimes issuing evacuation orders if the universe is inhabited, though that’s much easier said than done. Once the threat is resolved, or it’s been determined that the anomaly is not an issue, the class is removed.
All F class universes include a severity indicator. There are 7 levels of severity, 7 being the most severe, all indicated by an additional number following the letter F in the classification. (For example; F6-PK52O.) The F is always at the beginning of a classification, since it’s always the most relevant.
Each number corresponds with a specific anomaly threat level, those being;
1 = Benignant (Only used in special circumstances, where the anomaly's risk is known to increase under the right conditions. For example, FL-CONVERT's presence in a universe would mark it as F1)
2 = Quotidian
3 = Deleterious
4 = Periculous
5 = Baneful
6 = Virulent
7 = Calamitous
While Calamitous entities do in fact exist, no universe is ever marked with 7 thanks to the only two entities that ever obtain the title being both incredibly fast moving, and destroyed before M.U.E.C.I.F can properly mark any universes. However, they still keep 7 as a possibility, ‘just in case’.
Affiliated, Benignant, and Inscrutable anomalies are (usually) automatically exempt from marking universes as F due to their nature.
M.U.E.C.I.F urges people to not class nymtrott hives as F due to how common and relatively easy they are to deal with with proper equipment. This is also to prevent “oversaturating” the classification, and leading people to assume a major threat may just be nymtrotts.

G Class:

Universes with disproportionately more gases than solids or liquids, often forming with a sort of ‘universal atmosphere’. Most sophonts assume the atmosphere makes these universes more habitable, but they’re mistaken, as these universes tend to have a dangerous cocktail of gasses in them- some unique to the universe, and are therefor more dangerous than universes without one.
These are often considered an uncommon variant of K class due to how similar they are, but that’s not the case, as it’s rare for the same celestial bodies that form in K class universes to be possible in a G class universe. When this is the case, a universe is classed as both… but this is usually short lived unless there’s some sort of intervention (see P class.)
These universes are actually closely related to T class universes, and form very similarly.

H Class:

Universes that have been created artificially through some means. This classification is widely considered to be speculative in the local multiversal filament, with the exception of Serenus’ palace, which was created through unknown means.
However, this class is very possible- albeit rare and very situationally created.

I Class:

Universes that (usually) have a constant gravity everywhere in them and no other celestial bodies (again, usually). (Imagine an infinite, flat planet. Or… just ‘flat’ like a normal Minecraft world- but I couldn’t describe it like that in the actual books for obvious reasons no matter how much I really wanted to because it’s really hard to explain how these universes are otherwise.) They’re the most common type of universe and are almost never classed as a single letter.

J Class:

Extremely small “pocket universes,” ranging from the size of an average main sequence star to a single room. However, smaller have been documented on rare occasions.
These universes, despite common misconceptions, don’t last any longer or shorter than normally sized universes. They are however, less susceptible to unnatural universe fusions thanks to their size.
They’re very commonly paired with Q, P and V class.

K Class:

Universes that are created from a ‘spark’ of ximorenis and explode outwards from a single point, creating empty spaces between matter. K class universes are usually densely filled with stars and other celestial objects, but not always.
There is three types of K class universe; accelerated expansion, decreasing expansion, and standard expansion. Accelerated K class universes expand at a rate which causes them to be torn apart, decreasing K class universes expand at a rate so slow it causes gravity to collapse it in on itself, and standard K class universes expand at a non-harmful rate.
Standard expansion K class universes are the most likely to have intelligent life in them out of all universe classes due to the optimal conditions they create and their longer lifespan.
K universes are the most likely to paired with P universes out of all classes.

L Class:

Universes with one of a kind properties that are prevalent enough to be classed on their own. Mimic universes used to be classified as this before they were understood to be a common phenomenon.

M Class:

Universes that are still in early stages (Primordial era), and are still in the process of being formed. Also used for universes that are chaotic for non-anomalous reasons. Sometimes N class universes are mistakenly classed as this.

N Class:

Late degenerate and black hole era universes. (Once the universe enters it’s dark era, it's considered D class.)
N class also applies to any universe that is destroyed, dying or collapsed, but can’t be classed D.
These universes are frequently caused by the nihilgenesis during the events of the series.

O Class:

Universes which have their stability supported by a single object called a “core”. If the core gets destroyed the universe collapses in on itself. What the core is can vary a lot, but there’s two main types:
O Type 1:
A universe where the core is a large, star-like celestial object. This celestial object is usually the centerpiece of the universe, often being at the very center or some other obvious place. This is the most common type of O class universe since they’re typically more stable
O type 2:
A universe where any object could be the core. In universes like this the core could be anything from a paperclip to a planet’s moon. Anything the universe cannot survive without is considered a core. This is often, unfortunately, found out by accident.
This type of O class can sometimes have multiple cores as well. In cases like this, the universe will become more and more unstable the less cores there are. Sometimes, what the core is can change over time- but most people are unaware of this thanks to how impossible it is to track.

P Class:

Mimics that have formed as universes rather than standard entities. Every universe with viteroite in it is either P class, or was P class at some point before. The viteroite is often spread across the universe in patches (or as planets), and not all of it functions as a nucleus. Harvesting the viteroite usually doesn’t effect the mimic, even if it’s serving as a nucleus, since mimic universes tend to have thousands. However, of the mimic has very few nuclei, this could seriously harm or even kill it.
Most mimic universes either aren’t awake, or aren’t sapient, making it very hard for M.U.E.C.I.F to detect them. Some mimics like Rankine (PK52O) are able to create a sort of “avatar” for themselves, and move around physically within themselves, some being able to interact with the world around them. mimics like this may also effect the universe itself in more major ways- but most don’t bother with this and are more content with just observing things.
Historically, P class was used for universes that expressed ‘life-like’ properties since it was believed that universes couldn’t have Souls. However, with the discovery of mimic universes, this was changed and all universes previously classed P that weren’t mimics already were changed to something different.
P is most commonly paired with K and J. P class universes, very rarely, can spontaneously split into multiple universes, forming a pair of Q class universes and killing the mimic in the process (along with everything else living in the universe.)

Q Class:

Universes that are directly linked to another universe (if the universe it’s linked to dies, it dies.) This link is created through the universes being partially fused with eachother, or linked together by a sort of ‘thread’. This type of universe is very rare, and how exactly they form is a heavy topic of debate, especially because of how hard they are to detect.
These types of universes are harmless, and form naturally. A splitting P class universe can also create a set of Q class universes. Some Q class universes are a part of massive chains of universes- which has catastrophic results if one universe in the chain dies.
There is no link between C class universes and Q class universes, but it’s not unheard of for two Q class universes to fuse together- just understudied. This class tends to go hand and hand with type 2 V class.

R Class:

Universes that are constantly changing their classifiable traits, but stick to a few set rules. These universes have been damaged in some way, and are slightly unstable as a result.
M class universes are naturally this class for a short period of time.

S Class:

Completely unstable, ruleless universes in constant chaos. These universes, much like R class universes, are the result of universes being damaged. They are incredibly dangerous to enter, sometimes having progressed to a state similar to the genesis sea, and therefor impossible to live in.
S class universes, over the course of billions of years, will stabilize into an R class universe again, and eventually an N class universe.
These universes always have S at the beginning, and commonly pair with Z.

T Class:

Waterworld universes or any universe that contains disproportionately more liquids than solids or gases. These universes are related to G class universes, and are often very similar in how they form.

U Class:

A universe from a different timeline. This can be either a different version of an already existing universe, or a completely new one that’d only exist in said timeline.
These universes are purely speculative, but some theorize higher beings would be able to access them.

V Class:

V class universes are universes that you can stumble into by doing a certain action or going to a certain place. There are two types of this class.
V Type 1:
Constantly moves between universes and appears within them (Sometimes appearing in set conditions). They’re usually smaller and can be walked into without knowing.
Most of these universes are stray universes from the nearby Grey Multiverse, meaning an overwhelming amount of them are N or D class, and not often that interesting. Universes like this are usually short lived as well, having a tendency to harmlessly fuse into the universe they’re intersecting with.
V Type 2:
Acts similarly, but stays in a set location in the multiverse. Rather than the universe itself appearing within other universes, doing a certain thing in a specific spot, touching a certain object, etc will take you to it. It’s usually pretty noticeable when you end up in a type 2 V class universe. This class commonly goes hand and hand with Q class universes.

W Class:

Universes of multi-universal importance. Including, but not limited to; M.U.E.C.I.F’s home universe, their outpost universes, and The Stardust Palace.

X Class:

A universe that’s been discovered, but is yet to be or cannot be fully classed. This class may also be used as a placeholder while the classification is still pending.

Y Class:

A universe confirmed to be belonging to/from another multiverse. Very few universes of this class have ever been documented, and they're all overwhelmingly D or N class, being strays from The Grey Multiverse.

Z Class:

A universe with many incomprehensible properties, anything ranked Z class on its own or first is completely incomprehensible. Universes except for the genesis sea (and some VERY rare exceptions) with this letter high in the classification are unnaturally occurring.
A Z lower in the classification isn’t always a cause for concern, but M.U.E.C.I.F still recommends people stay away from them all together.

Universes commonly have more than one of these properties. The order of letters is always determined by which classifications are most important and prominent. For example; a universe with unknown properties that could be potentially dangerous would have X as its first letter, while a universe with unknown properties that are of minimal concern would have X as its last letter.
The number in the middle of a universe’s name determines how far away it is from the center of the multiverse (average number of universes away.) This serves to track the age of the universe, and shouldn’t be used to determine location.
“Ruins of reality” (DNLCZ990000~A) is the farthest and “The Stardust Palace” (WHGAJ1K) is consistently the closest. The center of the universe, “The Genesis Sea” (ZXLSM0Z) usually isn’t counted because of its complete incomprehensibility and absolute inaccessibility (and also because it isn’t a universe, it's the multiversal core! It’s just given a classification in order to be understood better.)
Type 1 V class universes and Y class universes are an exception to this and are given ‘#’ instead of a number. Any universes that are unable to be classed under this for whatever reason and aren’t type 1 V class or Y, use ‘?’.

The letter at the end of a universe’s name determines what type of life exists in it consistently and is the most relevant.
A: None
B: Only visitors from other universes
C: Only settlers from other universes
D: Only one to ten beings
E: Predominantly beings with B or C type souls
F: Predominantly beings with type A souls
G: Sapient creatures
H: Sophont creatures
I: At least one dominant sophont species (stages 4 to 6)
J: Majority avrunians
K: Majority deities or deities and avrunians
L: Early stage sophont species and avrunians, no deities.
O: Early stage sophont species and avrunians with deities.
M: Stage 7 sophont (capable of travel off planet or equivalent)
N: Stage 8 sophont (capable of travel outside star system or equivalent)
P: Stage 9 sophont (capable of harnessing star, universal core, or equivalent)
Q: Stage 10 sophont (capable of terraforming within reasonable time period)
R: Stage 11 sophont (has spread further than a lightyear from origin point)
S: Stage 12 sophont (Is the majority species in home universe)
T: Stage 13 (Able to exit it’s home universe without the use of gates or other outside forces)
U: Stage 14 or higher sophont that’s not deities or avrunians
V: Artificial life
W: Used to have life
X: Unknown
Y: Nymtrotts (this should be saved for exclusively nymtrott hives and heavily infested universes)
Z: N/A or beyond comprehension
(The most prominent trait takes priority, a universe cannot have 2 letters at the end.)

Blacklisted universe combinations

Some universe class combinations under no circumstances can be paired together due to conflicts or some other complex reason.
The full list of universes classes that cannot be together is:

Any class + itself
F on it’s own
W on it’s own
H on it’s own
P on it’s own
Y on it’s own
U on it’s own
O on it’s own
P + H
P + S
R + S
Q + C (a Q class universe fusing with another universe severs it’s connection to the other universes it’s connected to)

WarningSensitive Topics