Shattered Realms - a Homebrew Cosmology

[Caliban]

It kind of feels as though perhaps you have too many pieces going on here to the point where some things have become more than redundant. For instance the Interstitial planes all seem alike

Other than connecting to all the mortal planes, and then to the upper and lower planes in various ways, I don't see how they are all alike. The bright and spartan Plane of Mirrors, constructed out of reflections of the mortal worlds with mirrors; the dark and gloomy Plane of Shadows that connects to all the shadowy places; the Astral plane where physical matter is accelerated to the point where teleportation spells use it to achieve instantaneous travel and those who astral project into it can create materal bodies in other planes via the Color Pools. The Ethereal Plane, where ghosts and other incorporeal creatures dwell, a plane that you can observe without traveling there by using See Invisibility.

The interstitial planes are the connective tissue of the multiverse. Does your body need only a single type of connective tissue? They keep the other planes separated, yet allow travel between them using a variety of different methods.

Aside from all that, each of these planes existed in previous editions of D&D and are potential sources of plot points and interesting places for the PC's to explore . I don't see any reason to limit myself to just one.

... and, perhaps more troublingly, the idea that each of them connects all the mortal planes but since you included the elemental planes in that, it makes me wonder why there needs to be multiple ways of connecting all of them... Also, I have a bit of trouble conceptualizing how exactly you could have a plane that specifically connects all the other planes.

Why do we need multiple ways of traveling through our own world? I mean, we have walking, riding, cars, boats, trains, airplanes. Not to mention rivers, tunnels, cave systems, oceans, and roads. Basically, it allows for a "realistic" amount of fantastic travel methods in a fantasy settings. And as for conceptualizing how a plane can connect to all other planes...it's magic. Or N-dimensional mathematics. Take your pick.

Also, it makes me wonder about how it might work if you have multiple inhabitable worlds in a single universe, which it kind of seems like it should be a possibility. Do these connections only appear on a single world and if you live on a different world in the same universe you can't reach anywhere?

There are quite literally, an infinite number of inhabitable worlds in this cosmology, existing in an infinite number of mortal realms of various sizes. Some of the mortal realms only hold a single planet (or even a single element - such as an Elemental Plane of Air), while others contain billions of galaxies.

Maybe it is arguably more sci-fi, but I am thinking... even in a fantasy setting, isn't it possible on one world you can look up at the moon and see signs that people are living up there even though you can only see what is happening on a macroscale... or have legends that the blue "wandering star" in the sky apparently has people on it, and either way-- you can only get there by using magical doorways... Nevermind just how big a single world can be.

If there are people living on the moon, or even a nearby planet, then yes, it would be possible to see signs of them if you have the means of doing so via technology (telescopes) or magic (clairvoyance, auguries, etc.). Whether or not there are any inhabited planets near enough to see is up to the DM and the particular realm the campaign is set in. This is a cosmology - it comprises billions of universes in a single multiverse. Some of those universes are exactly like ours (well, ours with the added possibility of being visited by dimension hopping D&D adventurers).

So if you consider that the interstitial plane might be as necessary if not more necessary for connecting various parts of the same universe (in my example, the same system of the same star), how does that fit into this picture?

Not sure I understand your question. They work exactly as I described them. You can travel between various planes, or even various points on the same plane, using the interstitial planes. So you could use the Astral plane to travel to the High Heavens, to another mortal realm, or to another location on the same planet or to a different planet in the same realm (if the realm is one with multiple planets and/or stars).

Usually you don't travel to another planet in the same realm on accident. It's a long way, and generally it's much easier to use a well known path to nearby location or a nearby plane. Why would it be easier to travel to another plane of existence than to another planet in the same universe? Because this is a fantasy setting.

 

[Caliban]

Fantastic Features of Existence

Primal Core: The Source will occasionally eject a highly energetic clump of Primal energy, known as a Primal Core. Instead of being absorbed by the nearest nascent plane, it instead punches through the many planes of existence like a Meteor Swarm through a horde of goblins, leaving dimensional rifts and chaos in its wake.

As it passes through the Celestial Realms the gods themselves take note. For the lesser gods it represents an opportunity for advancement in the celestial ranks. A core of concentrated Primal energy can easily boost them from demi-god to lesser god, or lesser god to intermediate god status. For the Greater Gods it threatens to upset the balance of power in their particular pantheon, or cause a competing pantheon to become more aggressive as they gain a new source of power.

However, the Primal Core rarely comes to rest in in the Celestial Realms or the High Heavens. Instead it punches through them and cuts a swathe of destruction through the Mortal Realms before coming to a stop. Sometimes it creates an entirely new plane of existence, smaller in size that the planes that surround it, but one with far higher levels of Primal Energy, much as if a Celestial Plane had been transported to the Mortal Realms. This can disrupt the normal course of events in the surrounding Mortal Realms for thousands of years as Primal Energy bleeds from it into them. (This can lead to formerly low magic worlds gaining super heroes, or to Monty Haul campaigns in fantasy realms.)


Changestorms - also known as Chaos Storms, or Storms of Creation. Or “Holy , Run!” if you are caught in one.

A Changestorm is what is left in the wake of the Primal Core as it passes through a plane. The massive energies released by the Primal Core as it breaches the dimensional barriers cause unnatural storms to erupt throughout the plane, storms with the power to alter reality and remake the environment and warp or mutate any creatures exposed to the storm. It may even alter the natural laws of the plane, permanently changing how magic works, how sentients acquire skills, the strength of gravity, etc. (i.e. may be used as a plot device to transition to a new rule set or edition.)

The dimensional rifts may also pull creatures and even geography from other planes into this one, introducing a new sentient race or breed of monster, or creating/removing a mountain or mountain range. Non living things may become animated and even gain sentience, while living things may be transformed into stone or metal.

Creatures caught in a Changestorm may find themselves sent to another realm, transformed into a different race, they may be physically or mentally warped, they may gain new innate abilities or vulnerabilities. If these new abilities/vulnerabilities breed true and the creature is still recognizably of the same race as before the change, they are said to have gained a Bloodline ability.

Primal Seeds - also known as Creation Seeds or Power Seeds.

As the Primal Core punches its way through the dimensions, it leaves behind a trail of debris infused with the power creation itself. Some of these bits will quietly dissipate their energy into the plane as whole, others will explode with devastating effects, while still others will become trapped in the fabric of the dimension itself. When this happens, natural planar mechanism will seal the energy away (the planar equivalent of an oyster forming a pearl around a bit of sand). When this happens the sealed bit of Primal Energy is called a Primal Seed or a Power Seed.

Primal Seeds can take many forms, and may not even have a physical form at all - instead becoming a pocket of Primal Energy that can only be released under very specific (and sometimes bizarre) conditions.

Primal Seeds are potential incarnate - if a seed merges with a living creature (plant, animal, or sentient race) they often exhibit little or no obvious changes beyond being extremely long lived and healthy. (Although sometimes they will change drastically and become something altogether different.) Their descendents however will be exceptional members of their species, often becoming a more powerful version of that species with new abilities. (i.e. goblins -> hobgoblins; kobolds -> urds, human->ogre/giant)

If the Primal Seed instead infuses a non-living material, it may be transformed into a mythical metal such as Adamantine, Mithril, or Orichalcum - or it may appear to remain the same but become nearly indestructible. This can result in legendary weapons or armor crafted of crystal or glass, for example.

For the sentient races, the true value of a Primal Seed is realized when used to create a magical item. These often become items out of legend. If the Primal Seed merges with a person, often the Primal energy they are infused with transfer into items they craft or items they use for a long time. This is the source of the tales of legendary smiths, or weapons wielded by legendary heroes becoming powerful relics in their own right.

Genius Loci - Sometimes the Primal energy shed by a Primal Core infuses a piece of terrain. Such places of power are instead known as Genius Loci due to the fact that they usually have at least a low level of sentience. These are the spooky forests, the shadowy vales that are bigger on the inside, the floating islands, the living caves, etc. Genius Loci tend to attract magical creatures and members of the Fae. Many of them also serve as gateways to other realms, having formed around the site of a dimensional rift created by the Primal Core as it passed through.