To start this, a lot of CYOAs assign variable exact qualities to the same pool of words or concepts, which may be a sign of creative deficit but is also a natural consequence of having approximately the same theme. To clarify on ambiguous terms, I'm going to surround them with angle brackets, and prefix the name of the source CYOA with a colon.
If nothing is specified otherwise, assume that it follows the definition used in the source CYOA.
Information from later versions of a CYOA is prioritized over earlier ones, even if incomplete.

This document only covers planeswalker content, which will be defined as the genre where different worlds have different driving aesthetics to what is possible within them, and where it is possible for the player to visit worlds with those different aesthetics. Not all content featuring interdimensional travel is planeswalker, having an isekai intro would not automatically count, and neither would have having a multiverse of different histories.

We're also covering established CYOAs only, so fictional universes with the potential to fit into this genre, such as Dungeons & Dragons, Doctor Who, or Worm, also do not count unless they have a CYOA where there is an explicit option to leave the bounds of the defined universe (Magic the Awakening, ironically, does not qualify Magic the Gathering for this). Jumpchains do not count for this, and assuming that fictional factions have independent agency and growth potential is against its point anyway. Which reminds me, we are only covering NPC factions or factions whose leadership are NPCs, that is to say organized groups whose behavior can be predicted from written content without the need for reader intervention. So anything in this document must be:

• An interdimensional organization.
• From a CYOA with a mechanism for crossovers.
• Ruled by NPCs at some point in history.

Concepts

• Afterlife: One of the favorite topics in religion and fiction, and therefore wildly variable in this material. Most CYOAs assume that the afterlife is a phenomenon playing by versal rules, though other isekais will alternatively assume that resurrection in another universe (falsely labelled 'reincarnation') can be issued as an alternative to a planar afterlife. It is common in fantasy that an afterlife can be denied by certain sorcerers or predators, but not once you enter the afterlife proper. Planeswalking content oft has massive exemptions from that last rule whenever there's a multiversal threat, sometimes the players themselves, as the versal afterlife is expected to collapse alongside its ordinary counterpart.
  ** Living God mentions the existence of Planeswalkers dedicated to moving the deceased between afterlives, to keep death from permanently separating the deceased. The terms of this description are vague enough that it may either mean afterlives of an entirely different world, or afterlives of a different belief system.
  ** Ouroboros, part of the same shared universe, describes the afterlife, and religion in general, in Unitarian Universalist terms that focus more on personal ethics than cosmology, but also mentions that the Magna Nexus has constructed an artificial afterlife system for infinitely respawning their people into new childhoods. This enables their abuse of Human rights more than it preserves life. The creation of an artificial afterlife is also shown to be a possible feat for any magician that has mastered control over both fate and spacetime.
  ** Angel focuses on a rare example of a planar afterlife, or two. This depiction of Heaven is also Unitarian Universalist in its character, and stated to be incomprehensible for living minds to understand or appreciate. A potential inhabitant may choose the alternative reward of continuing to help the living as an Earthborn Angel. This stands in opposition to an equally or more vague hell, which has
  Angels can be divided into the alien Heavenborn that seem to rule or guard the afterlife, and the Earthborn that they recruit from the recently deceased
• Mana: The concept of 'potential energy' as applied to magical abilities. Usually takes on properties of both a background radiation and a vapor, but can be accumulated by objects or people without changing their physical properties. Sometimes an environmental property, sometimes needing to be generated from completing certain actions. Additional properties of mana are variable.
  **
• Planar versus Versal: The differentiation in a CYOA between locally granted powers in a specific setting and those that are elevated to a multiversal constant. This is a defense mechanism against the very sort of crossover wank that we're about to indulge in. Versal powers are tied to a specific universe and are difficult for a walker to project into other cosmologies without some extra factor, whereas planar powers are projected by either an external cosmic entity or
  ** Magocratic Convention: Blood, and Conventional, magic are the only forms of planar magic known to the Convention, though the Convention has various tricks to access, project, or even create versal magics. Borrowing access to the local versal magic only requires certain Entropic spells, but the latter two are feats of spiritual engineering ('sorcery' in their terms) that demand immense magical resources to manufacture.
• Planeswalking: Travel between universes with a different governing theme or 'genre'. This is either enabled by some external invention, or an intrinsic 'spark' of the user's corporeal or ethereal body.
• Void: A plane that lacks any sort of intrinsic contents or features, making it inherently hostile to the dependance of all things on other features of the environment. Because it has nothing to it, it can only be described by the consequences of its interactions with other universes.
  ** Blood Magic: The exploitation of the void, by drawing the world closer to it through sacrificial practice, is the core of Blood magic. There are also multiple externalized instances of voids, called 'souls' in the system of Blood magic, that relate to their bearers as a traditional soul would. These inner voids are the most expensive sacrifices that a blood mage can make, and cause the Void to directly open into the world with devastating effects, possibly permanently if it is repeated. This permanent damage has been described in similar terms to how it works in Wanderer of Broken Worlds, as seen by the examples of Irkalla and other battlegrounds of the war between the Convention and Abysswalkers.
  ** Planeswalker Rising: The Void is an element inside the XXX's system of elements, which also anthropomorphized as 'death' in their system of thaumaturgical patrons.
  ** Wanderer of Broken Worlds: The Void is the antagonist of this CYOA, a corrosive existential force that is warded from universes by their 'barriers', should it be lost or damaged, the world is then opened up to any kind of destructive phenomena, and also to entry from those who call themselves Travellers. The travellers (not to be confused with the protagonists of traveller's tale) are those who bear a 'traveller factor' in their souls that allows them to survive it, as a benefit of having souls that are contaminated by Void, which comes with other potentially beneficial abilities.
• Sphere of influence: The ability of a planeswalking organization to access other universes, which is expected to bear heavy influence on their ability to interact with other organizations.
• Magic: Abilities tied to non-biological facets of the user's own being. I don't like the following simplification any more than you, but we're counting any sort of 'psionics' or superpowers as magic for the intents of this discussion. The scientifically and technologically granted abilities of Doctor Manhattan would be magic if he were here.
• Technology: Abilities tied to external objects of a usually inanimate nature. These are oft called "artifacts" or similar if their existence overlaps with the rules that govern magic, and will be inserted into this section even if they were described as magic by the CYOA.
• Manpower: The access of the organization to intelligent underlings, with or without planeswalking ability.
• Politics: Structure of the planeswalking organization and how its attitudes have affected such.
• Relationships: Predictable interactions with other organizations based on their behavior and beliefs.

CYOAs

• Angel (Heaven, Hell)
• Entropist (Fathers, Daughters)
• Blood Magic (Ark, Convention, Eclipse, Enforcers)
• Traveller's Tale (Travellers, Wyrm-Whales)
• The Tokverse
  ** Nemesis (Invidia)
• Power Creator multiverse / Verse
  ** Living God (Grand Empire, Oblivion Compact, Lithic Empire)
  ** Ouroboros (Tribunal, Guilds, Magna Nexus, Philogony, Sapiens Systems)

Basic concepts

Takes on the multiverse are all wildly variable, however, they all share in a few basic concepts here in CYOAG. First there is a place where everything happens, which encompasses everything that you're properly interacting with, all its people and planets and stars. Second there is a place where nothing happens and it has no other qualities to mention except for it interactions with the first place, which is usually by obstructing it, being caustic to it, and probably powering gnarly magical powers.

The first place is existence and the second is the void.

Existence supports matter and objects inside it according to various rules that vary between universes, and the shifts between these rules greatly complicate potential interdimensional travel for their differing laws of physics and metaphysics. However, Ultimate God and Magocratic Convention state that it is made from a constant set of concepts, no matter how magic or technology or nature may work inside of it.

In Magocratic Convention, these are the four elements of the Unknown (hidden information), Real (magical and physical energy), Unimaginable (dimensional fabric), and Imaginary (human biases). The Convention admits that its model is not in its final shape, that spells have been reclassified, and that spells have been found outside the four element model. What we're seeing is more like an alchemical glossary than the periodic table, in terms of sophistication.

While in Ultimate God, there are twelve Aspects borrowed from Homestuck that make the contents of all universes, which will always be mentioned by their Homestuck names. FYI that means that Doom is the opposite of Life, Void opposite of Light, and Blood and Breath admit to their elemental themes.
This document typically assumes a severe level of narrative unreliability, but it's safe to agree that gods who make universes do understand their job, so we will take this model as a completed version of the one that the Convention uses.
The Entropic element deals with probability, supernatural favor, and forms of energy that include literal light. It's hard to disbelieve that it represents the Light aspect.
Planar element magic can also fit into Space without any argument, except for its Spellcraft that represents time control, but I won't even argue that they're misclassified Time spells, only time-related effects that run on Space magic. I'll later return to the question of what 'Time' 'magic' really is.
The Arcane element is easily Void, although Tankistaheads will balk at this because an entirely separate type of magic leverages the multidimensional Void in the cosmology of Blood Magic CYOA.
Finally, the Conceptual element is Hope aspected (bastardized by Aromage into 'Creation') when Conceptual spells are the most similar to the powers of traditional 'angels' (Hopeforms) dealing with events that are difficult to objectively define, I.E. things which most people have FAITH in.

Ultimate God also says that all mortal beings are a living expression of one of the Aspects, and puts them into categories named after those embodied Aspects with -form suffixed after it. This gives us a handy way of classifying supernatural creatures that has a few duds but otherwise covers most cosmically important creatures:

• Lifeforms obviously covers any normal living creature and a few extraordinary ones.
• Doomforms are the undead.
• Timeforms are ensouled, 'living' machines.
• Hopeforms are angels.
• Rageforms are demons.
• Voidforms are eldritch abominations from the interdimensional vacuum.

The last is the most important addition because they're never given the same name whenever someone reuses this plot, and there are other plots that can introduce an 'eldritch abomination' that can embody any other aspect. 'Hopeform' and 'rageform' are here for a similar reason; to draw a distinction between 'real' spiritual beings versus lifeforms (or whatever other form) that are just themed after them.

Going forward, we'll guess that there are three different kinds of planar abilities; being part of a biological or spiritual species that can project planar abilities from either its soul or another universe, leaning on an extradimensional patron being (using the prior category by proxy), or manipulating one of the multiversal aspects. We've covered four kinds of magic that fit into the latter category, what are the others? Psionics (as in seen in Dawn of a Planeswalker) fits into Mind without any argument.

Blood magic (Magocratic Convention), in a turn that will only surprise Tankista fans, lives up to its name. You see, Blood in Homestuck is the Aspect of relationships and connections just as much as literal blood, and Blood Magic makes frequent references to sympathetic and symbolic connections between objects, even more than literal blood.
Blood magic deals with sympathetic connections between life forces and objects, to exploit the Void, which is the same thing as a 'soul' according to them.

Their unique and narrow definition of a soul describes it as a piece of Write-Only Memory, which fits into the purview of Homestuck Void as the Aspect of both obscurity and nothingness, so it's the one twelfth of a soul that is Void aspected, and this function is so arcane that its removal is seemingly a harmless action. Then the Void must be the write-only memory of the entire multiverse, which contains all the 'junk data' that couldn't naturally or safely fit into its narrative. Blood magic, in all its other forms, evolved from the magic used to summon rageforms from nearby planes (or any other kind of creature including - theoretically - lifeforms), but was repurposed to summon predefined impossible events from the Void in exchange for a certain amount of living potential. This is the same reason why a sacrificed soul continues to exist inside of the Void; because sacrifices in Blood magic are currencies, not fuel. (Note that I'm not saying that other planar systems are extensions of Blood magic through conventional magic, rather, Conventional magic works by creating a sympathetic matrix between the Aspects inside the user's soul and their surrounding reality, which they manipulate by transforming a certain energy into those Aspects.

Technology, when it hits the multiversal stage, deals with the Time Aspect for a plethora of thematic and logical reasons; time and technology are both associated with the future, time travel based multiverses more frequently have science fiction aspects, technology is about repeating material events to achieve a desired end, and that's their aesthetic in Homestuck.

The Sons and other users of 'soul magic' in Entropist are the Heart users, who dissassemble souls to use their component aspects as resources, possible modifying their own to project versal systems as many other kinds of planeswalkers do. It may be the afterlife simulations from the Nxtub-verse that are Doom Aspected magic users, who create an imaginary destination of the soul to generate it from the expectation that it is the fate of the user's soul, but then, I haven't read enough past Seinaru Magical Girls to accurately describe this and I'm just going off of someone else's theory at the moment. It could just as well be a kind of Mind trick. Either way, Seinaru Magical Girls fits very well into the cosmologies of both Wanderer of Broken Worlds (as a representation of a main sequence world) and Magocratic Convention (as an example of universes being generated by code), that it's practically an unofficial link between them.

Depictions of the multiverse have another curiously consistent quality; it's not hard for a planeswalker to duplicate a universe by successfully using time travel (Blood Magic, Conduit, Planeswalker Rising, Traveller's Tale 2). The last two even say this is the only outcome of any attempt at planeswalking into a place of interest. Planeswalker Rising and Magocratic Convention both say that all 'real' universes are surrounded by an infinitely dense cloud of alternate timelines, none of which have the ability to make observations or tangible interactions with the outside multiverse. They are more like ideas than places, memories of what could have been, until one steps into them from outside. This occupies an apparent hybrid position between existent and non-existent, outside of reality like the latter, but structured and coherent like the former. This is the natural counterpart to Perception in Blood Magic (just like its counterparts in consciousness, biology, et cetera), the connection between a universe and its surrounding void organizing the latter in its image through the bleeding effect. This is responsible for another common phenomenon which is the resemblance of the multiverse to outer space from the perspective of an interdimensional traveller, each universe shining with the unintelligible information inside of it.

Parachronozoids and other Outsiders

Material in this genre is also chock-full of interdimensional 'monsters' that an explorer should be wary of, which may only be told about from other magical beasts by their ability to travel between dimensions, and

A planeswalker is just a humanoid parachronozoid, hiding its true nature by being materially identical to a normal humanoid.

Clade (CYOA)

sphere of influence
origination
ecology
behavior
abilities

Planeswalking organizations

Faction (CYOA)

sphere of influence
magic
technology
manpower
politics
relationships

Dark Lords (Dark Lord)

This makes me feel like it's an HFY CYOA, where /you're/ the inhuman bad guy.

The Convention (Blood Magic)
The Convention is a vast interstellar bureaucracy dedicated to protecting the multiverse against dimensional imperialism, eldritch abominations, and forbidden knowledge. They began as a Covenant of Blood mages that turned on the practice at great cost once an alternative power source was finally discovered. The secondary benefit of this alternative source, was the means to find areas where the universal mana field naturally accesses alternate planes or even universes - far less expensive than creating one by the Outer Gate spell.
While their draining operations in preparation for vast and unknown threats have stereotyped them as a ruthless mass murderors, +this has never been canon+. Essentially they would transport the entire population into an alternate universe, sorting the subjected world for the subjects of their campaigns, and then split the original plane. Even the related policy only regulates the +option+ to retreat from saving a world in the most dangerous and horrible disasters. They are not cruel or genocidal, but simply utilitarian.

sphere of influence

The influence of the Convention emanates from the post-scarcity 'plane' they call Eden, conquered by Saul, the Second Omniarch, when he was transitioning them from a Covenant to an interdimensional government. From thence do they maintain a network of gateways between the numerous worlds of what they boldly call the "Observable Multiverse". These gates are active at certain chokepoints in the world, even if they have chosen to station their assets in some other, inhospitable area. This can be seen in the position of their units in 'Blood Magic', as their 'temples' were primarily located in Sheol's Antarctica while the gateway itself was in Australia. It is indicated in 'Hell Rebellion' that other types of dimensional traveller do need to use gateway sites, namely the eldritch invaders, and explains the presence of funky calamari in the Indian and Pacific Oceans of Sheol.
Planeshifting fails on both sides without mana, which has allowed the Convention to maintain the illusion that they're not using Planar Splits, and shielded factions of Sheol from Conventional interference after the conclusion of the Covenant wars. Traveller 2 identifies their system as the same 'Inter-Reality Ley-Lines' used by Conduits, although Magocratic Convention itself describes an Gateway as an artificial construct that is ejected from the spirit of its user to assume the job of a permanent entrance into another world. It appears to be the case that a Gateway needs to consume native mana or else it will cease working, which is why various native Covenants were able to cut off the Convention's access to Sheol.
Planes of interest to the Convention are named for the various locations of mythology. This line of thinking has a hellish slant even if the plane is prospectively normal, as shown in the case of 'Iriy', the world of Time of Troubles.

magic

The Convention uses a namesake refinement of Blood magic that wields a more traditional power source, at first glance. While still sacrificial in nature, the relationship between between Conventional and Blood magic is like dividing a stab wound into the units of discomfort that you feel from one grain of sand in your eye, and then spreading this experience to thousands of strangers. It only matters to very autistic utilitarians.
Conventional magic has been divided into four 'elements', which are not components of matter, but of the universe itself in their theories. All of them have some mix of defensive, offensive, and utility abilities,
Entropic magic is the most simple and straightforward of the elements, governing both mundane and supernatural energies of the local universe. It ac

However, it is reasonable to suggest that this is not a unique problem with planar telekinesis and the Convention just happens to be the one organization that measured how they were pretending to break conservation of energy, similarly to the way that only first world countries are willing to scrutinize their environmental impact.

politics

In these discussions, we will assume that anything which:

leverages the Void to the detriment of the universe
is exclusively powered by a sacrifice
summons objectively evil spirit creatures

...is going to be treated like Blood magic whether or not it fits very well into Tankista's magic system, because it's not a problem with the system of Blood magic, but the attributes of that system, which are cliches with dark powers in general.
To clear most unknown variables, we're also assuming that the Convention is in the state shown in Blood Magic, where it is desperately trying to evacuate Sheol's Covenant wars

And now for CYOAs which aren't multiverse /genre/ but are set in a multiverse.

Seinaru Magical Girls

Witch Awakening