To understand where the parasitic universes come from, one must first look at the void between the universes and how we bridge it. The bridges between universes are normally initiated from one side, and necessitate an extension of that universe through the void between them, to another universe. However once the link has been initiated, the target universe will extend along the link to the host universe, and the bridge will become a commingling of the two. Universes are not meant to live alongside each other like this, and both will need to keep supplying energy to maintain a stable bridge.

However, even with this energy, the bridge itself will constantly be in flux as the two universes vie for control in a hysteresis of laws. This is a violent and volatile system and often small parts of the bridge break off and float away into the void. These are the seeds of the parasitic universes. Nearly all of these seeds will wither and die, or be re-assumed by the bridge. Very few survive long enough to become a universe of their own.

Those that do survive, that undergo their own expansion, will inevitably drift and connect to one of their parent universes. It is here that the term parasitic comes into play. For these universes require energy, matter, life from their parents, prolonged connexion will rob the local area of the connexion point of all these things, making it akin to the void.

These connexions are commonly and erroneously called the dungeon gate. It is this quirk of terminology that leads on to the truly surprising thing about parasitic universes. They are not just simple acts of nature, but instead have always been found to contain an intellect. They are in a word, sentient. This sentience appears normally in the form of a crystalline structure, one which has informed much of the science about artificial intelligence in recent years. It is this structure that takes the moniker "Dungeon core".

What the core wants is to become real. To become its own universe, self-sustaining. How many of them actually manage it is a question we cannot answer. There's more universes out there than those we know of and a parasitic universe could attach itself to any one of them and take its place in the multiverse. There are strong theories that this is the case, for most magical universes, as every parasitic universe discovered has been magical in nature, but seemingly happy to "feed" on mundane universes. It seems inevitable with this knowledge that all universes, eventually will be magical.

There is hope however, these parasites are not invulnerable, their appearance not the inevitable harbinger of doom. They have a weakness, and it is the dungeon core. If this is destroyed, removed, or otherwise contained, the parasitic universe will collapse and disgorge its stolen reality back into the host universe. The cores are of at least Human intelligence and know this too, which is why the destruction is left to highly specialised teams of warriors.

A parasitic universe is born from a seed, and will continue to exist until it is destroyed or exhausts its entropy. The seed has only been observed to be created by the flux around the centre of a trans-universal bridge*. This seed will most often be re-assumed by the bridge as the flow of reality into the void between universes wavers and encounters the seeds, destroying them. The rare seed that escapes this destruction is often left adrift in the void, and will exhaust its entropy before it can establish itself. There are an infinitesimal few seeds that manage to find a host universe.

Most of those will probably never be found, attaching themselves to areas in deep space and budding off when they've got enough entropy to survive. However, extensive re-examination of astronomical data has shown that there are very few detectable incursions in recorded history outside the Earth. Speculation about this has been rife for centuries, but it appears that in some way, the presence of life attracts dungeons. This could easily have been an issue for us her on Earth, as many places where life exists are antithetical to human life. Most notably the deep oceans and the central plateau of Antarctica. However we have an ally in all of life. The effect of magic on humans is noticeable, gross morphological changes are common and obvious, exposure to mana also appears to grant the ability to manipulate this new resource as well. This effect isn't only confined to humanity, it's also seen in other species. In the deeps, the microscopic life forms appear to react to mana by becoming manavores, voracious ones. Any dungeon gate forming under the seas is rapidly infiltrated and destroyed by the sea water and the life therein. The frozen South, somewhat more frozen since the North fell, presents a different problem. Life there is often deep under the ice, as are the dungeon gates. Here we've had to deploy a sensor network all over the continent and specialised teams have to mine through the ice to deliver their loads of divers.

The interiors of the parasitic universes appear to also all be remarkably similar to the Earth. There's almost always an atmosphere, very often it's within Earth climatic norms and composition. The atmosphere is a mixture of gases, and often saturated with mana too. The gravitic forces, which there also appears to be no reason for, are also generally very close to that of Earth standard, with variations of more than five percent each way being in the five sigma range of rarity.

Oddly the most common shared attribute is the presence of life, which is not the same as the Earth's. The Earth's life is naturally evolved and is not a result of magic. The parasite universe's life is a result of the interaction of the two worlds that formed its seed. The interaction is not always obvious, but it is always possible to see the effects of magic on the lifeforms within. There's a strong trend to the fantasy tropes of Earth, kobolds, goblins, kappa, and the like. It is theorised that seed contains some of the information from each world, or that the stories of old were spawned by naturally occurring bridges creating dungeons in pre-history.

The monsters, and let us be clear these life forms are nearly never sentient (see appendix 1), are analogous to the immune system of a terrestrial lifeform. They will attack intruders on sight, if given an opportunity to do so they will sortie out into the world and attempt to harvest any lifeforms around. This can seem incongruous when the Divers Association are called to deal with ogres who are picking flowers by the armful and rushing back into the dungeon with them. However this behaviour is exactly the same to these lifeforms as rushing out and grabbing any local people or animals would be. They do not appear to differentiate between animal, plant, fungal or even human lifeforms. They just grab whatever they can find and take it back into the dungeon. The life is then killed if possible near the core, which appears to gain something from this process.

The mindless and predictable actions of the "antibodies" of the parasite universe are often exploited by the Divers. The Divers are, of course, subject to the Lee-Gygax system (hereafter referred to as "The System", as it commonly is known) that all humans exposed to magic are. This allows them to gain 'XP', or experience points and level up. Leveling up and the vagaries of The System are beyond the scope of this paper and further research is required. There are several grades of "antibody", the commonest being classified as 'Trash', then there are the 'Elites' which are roughly three to four times stronger than the Trash. The Elites are found at a ratio of one Elite to approximately twenty Trash, or a little under five percent. There also exist the 'Masters' which are the most powerful of the Elites, and the 'Supreme' which are the most powerful in the dungeon. Only rarely will a dungeon have more than one Supreme, but it is possible.

This leads on to the categories of dungeons, these refer to the strength of the antibodies and the size of the dungeon. Size here is deceptive, as it refers to the absolute interior volume of the parasitic universe. The explorable or active part of the dungeon can be smaller in a higher category than a lower, but the volume will be greater overall. The core has greater capabilities the higher the category, and the strength and power of the antibodies is also affected.

Category 1:

A parasitic universe of no more than one or two galactic volumes.

Time will pass in here between forty and sixty times faster than outside

The core can generate some small traps, physical only.

antibodies are weak, translating to levels one to five of the system.

Category 2:

A parasitic universe of no more than four to eight galactic volumes.

Time will pass in here between thirty and forty times faster than outside

The core can generate some small traps, no more than five percent of which can use magic.

antibodies are weak, translating to levels five to ten of the system.

Category 3:

A parasitic universe of no more than one local cluster volume.

Time will pass in here between twenty and thirty-five times faster than outside. (Note, overlap here means that time cannot be the sole factor in determining category)

The core can generate some small traps, no more than ten percent of which can use magic. One or two large traps can also spawn. It can control elites and higher directly.

antibodies are stronger, translating to levels ten to thirty of the system.

Category 4:

A parasitic universe of no more than two local clusters in volume.

Time will pass in here between ten and twenty-two times faster than outside

The core can generate many small traps, all of which could be magical. Many large traps can also spawn. It can control elites and higher directly. These elites can work in concert.

antibodies are strong, translating to levels thirty to fifty of the system.

Category 5:

A parasitic universe of no more than eight local clusters in volume.

Time will pass in here between five and seventeen times faster than outside

The core can generate many small traps, all of which could be magical. Many large traps can also spawn. It can control elites and higher directly. These elites and masters can work in concert. The core here will be significantly more intelligent than an average human.

antibodies are strong, translating to levels forty to sixty of the system.

Catgory 6:

A parasitic universe of no more than sixteen local clusters in volume.

Time will pass between three and seven times faster than outside

The core has started to manifest its own body, the Supreme of the dungeon.

Categorisations beyond this point are strictly conjecture, as far as we know, anything could be possible.

*This author contends that when two universes are joined, they become one universe by definition. This is not the commonly accepted definition, however it has the advantage of being strictly correct.