The Silulis is a ghost data realm that contains imperfect duplicates (backups) of the Lathrym and Ersis. It exists beneath, and yet all around, the physical realms. Aeri, Aebys, and Aelo all originated from The Silulis, as well as the Eelekti and the Shades. The realm is home to The Silulic Horror, and is the source of Dekn Silulic Manipulation powers.
The Silulis was formed by .Mainframe some time after the physical realms were created. Any time the universe was manipulated or added to, .Mainframe would replicate that addition in ghost data form. Eventually, .Mainframe was renamed The Silulis, and came to be regarded as its own realm (known as a super-realm).
While the Lathrym encompasses the empty space beyond Ersis, The Silulis encompasses everything underneath (and yet also around) the Lathyrm. The Silulis consists of a realm which act as a date duplicate of the Lathrym.
The Silulis is primarily a very dark, ghostly inversion of the physical world. Its atmosphere is foggy, and has an almost underwater feel to it. A mucus-like substance spiderwebs throughout various portions of the realm (allegedly a bi-product of an ancient abomination moving about), and the ground has a soft, mushy feel to it. Odd echoing noises sound throughout the realm, originating from massive beasts that soar through the skies, too high up to be seen. The Lathrym Silulis is the same size as its real world counterpart.
For reasons unknown, the Ersian Silulis is a jumble of the various environments found on the Seeds: a cross-stitched world of impossible biomes, with equally impossible flora and fauna. A frozen jungle is as likely as a hurricane-ridden desert; an ocean might be full of molten lava, while a volcano could house a beautiful forested Eden. One might run into a pack of winged shark-wolves, flying whales covered in plated armor, or an elephant with a snake's head. While it hasn't been mapped in its entirety, the Ersian Silulis is estimated to be the size of five Milky Way Galaxies (possibly echoing the five Seeds of Ersis).
Aeri, Aebys, and Aelo
Aeri is a type of dark matter air that originates from mega-organisms that dwell in the Silulis. The Aeri seeps into the Lathrym and provides a breathable air for the beings within it. Humans are also able to breath Aeri (though it can be physically taxing for them)
Aebys is a water-like substance, originating from the residue that forms on the stringy webs throughout the Silulis. It is denser and thicker than Ersian, but very murky and blackened, making it difficult to see anything underneath the surface. It is very similar to Ersian "heavy water". Aebys has pooled into the Lathrym in various places, even forming an ocean within the Elevrium.
Aelo is a grass-like substance that is actually a parasite in the physical world, feeding on megafauna beneath the ground of the Silulis. It has an appearance like grass, and varies in color. Its presence in the sub-realms varies, as some can have it and others might not. Because of its appearance, it is considered a plant in the Silulis.
The Silulic Horror
The Silulic Horror is a massive Ethric beast created by the Hethe Ced'ric. This creature is the source of the spider's web of mucus-like strands that crisscross the Silulis; these strands contain proteins and nerve endings, and stretch millions of miles to the Elevrium. The being known as "Jacques" taught the Dekn to use their horns to forge a mental connection with the Horror; through this connection to The Silulis, the Dekn are able to manipulate objects by moving their ghost data duplicates, creating an effect similar to telekinesis.
The Eelekti, or Elective Data, are featureless humanoid beings native to the Silulis. Some are sentient, sapient beings, while others are empty husks that serve as recreations of other beings from Ersis and the Lathrym. Dekn manipulate inanimate objects in the physical realms by accessing their own Eelekti husks in the Silulis.
The Shades are former Arkn Eelekti that have evolved into an independent race of clay-like, sapient, sentient beings. They eventually fell out of the Silulis and into the Lathrym. They are more humanoid than other native Eelekti, possessing facial features and other distinguishing characteristics. They currently have two permanent settlements in the Empyrium (Ravatro and Ankluxor) and many travelling colonies.
Most living beings are unaware of the existence of the Silulis. The superrealm can only be accessed by going off the edge of a realm or sub-realm. Sub-realms essentially form bubbles between the Silulis and the worlds above, which can be entered through tears in the Lathrym; entering a tear incorrectly can cause one to end up in the Silulis.
If a non-native being enters the Silulis, they will have a limited window of time in which they can escape; the longer one remains in the realm and the deeper they go into it, the more intangible and ghost-like they'll become, gradually fading away until eventually they become trapped in the Silulis. Furthermore, the longer one remains in the Silulis, the more aware horrors of the realm will become of their presence and the greater their chances of being eaten (which can occur even after they become intangible). The only way to escape the Silulis is to make it to the opposite side of the sub-realm one fell into and crawl out by the edge.