New Considerations on Rat Kings
There is much already known about Rat Kings, of course. We know that they are carriers for lycanthropy, specifically that they produce wererats. Their bodies are indeed made up of multiple rats, and they are known to use their amorphous forms to entangle their victims, restraining them so that they may attack them further. They are undead of some form, though it seems to me that their origins are perhaps more nebulous than common superstition would indicate.
Common superstition suggests that rat kings are made by the souls of the hungry after famine, combined with rats that died from starvation. However, further inquiries seem to suggest that this may well be an oversimplification of the creatures. Though they do seem to carry common traits of the undead, they seem to carry a certain level of sentience and intelligence that is not ascribed to a common rat even. In meeting one, it showed emotions that are not commonly ascribed to creatures: most specifically rage, desire, and loss. The creatures can communicate, albeit strictly in abyssal, which is certainly possible in some undead, but not common among undead that is formed of non-sentient creatures. While certainly the argument can be made (and I would expect it to be) that the souls of the dead that inhabit it provide that spark of sentience, I am unsure that it is so simple.
My most recent meeting with a rat king brought me through one of these doors that have appeared throughout the land in recent months. The Creature seemed to be native to the place within this door, and it seemed to draw some form of power in the place it stood. This provides evidence of an origin beyond that of normal superstition, and perhaps even one that goes beyond the nature of the realm itself.
What is more interesting is that the creature may well be the origin of the Door itself. With so much focus on closing the gates, others who follow on adventuring paths seem to forgo a far more interesting and far reaching question: Do creatures from these other planes (or dimensions) unconsciously create the doors through some sort of need? Is the realm itself responding to the wants and desires of the creatures and opening the doors because of them? It seems too likely to just be coincidence.