Note: First numeral dictates original version. Second version is the Jasyn Jones revision. Third is based off of ETERNITY's revision of the Axiom system.
Magic: 13/15/14 From the start, the Underground has existed as a place for magical beings. There is nothing inherently fantastic about magic here, even if its skillful application is a common and easy source of awe. At the cutting edge of the science of magic is the awareness of Earth's fringe realms. However, their models of interdimensional physics are extremely incorrect and tinted by their relationship with Core Earth and its inhabitants and ignorance to the Everlaw of One.
Social: 20/15/20 While evolving at almost the same speed as Earth, the Underground doesn't have a large enough scope or population for many of the higher effects. Memes and the noosphere are a decently understood concept.
Religion is not an important part of the Underground. Their understanding of metaphysics is rooted in other axioms.
The Underground is equal to Earth in terms of ordinary technology, however, side effects of its world laws allow the existence of Weird Science up to 26/22/25. These devices are much more energy efficient than Nile Empire and Terran counterparts even if their technological limits are more significant.
Law of Polarity: Two memes in conflict grow stronger off of each other, pushing many Cosms into writing eternal war into their world laws. However, the Underground is unified by its hatred of the human race, the only "other" that it knows. As such, the Underground subtly changes itself to oppose the reality and "alignment" of the beings who enter it. The Honorable face a conniving and treacherous underground, the Evil are swarmed with do-gooders. Only someone with 2 or more adds in Faith (Zinatt) can avoid this through their balanced nature. While Possibility Energy is normally red AND blue, this law colors it based on where it comes from. The Core Earth natives present here make even the native energy slothful and hopless, turning all possibility energy unnaturally corporeal and allowing weird science.
Law of De-Termination: The stormer with the highest combination of their Reality skill and amount of Possibilities is able to fake time travel by leeching off its connection to Core Earth's immense amount of possibilities to transform it into an earlier version of itself as long as they can remember and comprehend that time. Everyone caught in this event has their "future" self folded into the subconscious, even the person who did it only remembers it as a possible decision or intrusive thought, which makes "forward" "time travel" an impossibility. This ability costs 3 Possibilities and can be done at any moment, even immediately after any kind of death.
"Monsters", the inhabitants of the Underground, are less real than other beings. They're the only surviving remnant of a religion that has been dead for centuries, flickering shadows living on through their separation from a long dead world. Only transformation to a different reality can be able to save them from the lethal consequences of disconnecting from a high magic reality. This affair is complicated by how even an ord has greater supplies of possibility energy than monsters, they'd be destroyed by transformation without an external source of possibilities. Even p-rated monsters can only have a single add in Reality, and can't spend possibilities except for using special abilities such as Martial Arts or preserving their own life. But, their unreal nature makes aspects of their existence aside from fundamental personal reality easier to change as well. Training with possibilities only costs twice the amount of weeks needed to learn skills instead of thrice. At the moment of death at a dramatic scene, a p-rated monster can also de terminate at the expense of all their possibilities and transform into a version of themselves that has been optimized for the situation. All their skill adds are doubled and they're fully healed. They will die at the end of the scene.
While the Underground supports Conjuration, most monsters /conjuration substitute/ with another one of their main skills. Additionally use Lightblight rules for monsters that are forced into a world that has Magic 10/6/13 or less.
Finally, some of the Gaunt Man's agents speculate that religiously oriented low-magic realms are so idyllic (by native standards) relative to other cosms because they define themselves as being in opposition to weakened or nonexistent beings and thus the Law of Polarity is just an extreme edge case of this property (humans being the monster's "demons") and barely a world law.