Introducing the Ossoviso! To summarize, the Ossoviso, or Oss for short, are beings created in the Void before any universe came to be. They can travel between universes, slip in and out of realities at their leisure, and generally just enjoy messing with non-ascendant beings for fun. While being incredibly mischievous and clever tricksters, the Oss are not inherently evil or capable of malice without some sort of outside influence or control. Details below.
Amazing art done by  Ninora-Art
This is an OPEN SPECIES with the intent for anyone to go and make their own. Get creative! The character depicted, Cheddar, is mine, though.

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APPEARANCE

The Oss are most notable for their bone-plated faces, feral-type lizard form, horns, and glowing patches. The bone-face and horns are universal, however the number and style of horns are completely open to change, with one rule. The male Oss all have curved, ram-like horns, and the females have horns that stick out and back, like a dragon. The number of eyes, arms, legs, tails, and just about everything is adjustable. Bone plates may also be placed anywhere in any multitude on the body, as well as the fur, except for the belly/underside. Glowing stripes and such are indicative of nerve clusters, i.e., sensitive areas they can feel more, such as hands and fingertips. Colors for everything are customizable. Oss can have skin or scales, but when viewed up close, one can see stars and space within it. Fur and hair are dotted with pinpoints of light, glowing from within.
Oss are not always feral in stature, but it is their default state. Anthro is available.

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BEHAVIOR

Most Ossoviso have an inherent, great fascination with the lives of mortals and being stuck in the third dimension. They take great care to, when interfering, not completely ruin anything. Oss will approach a person, or, more likely, pull them into a pocket realm and offer them a contract. The person can ask for anything they desire, so long as it affects solely them, and the Oss can work with them to come to an agreement. The cost is always vague and oftentimes an experience rather than an actual price. The Oss are merciful to the kind and good-willed, and find joy in pissing off the selfish or wrong. Their prices usually lead to a revelation or moral lesson for the person. The Oss cannot and will not kill.
They like to live underground, in dark, wet cavernous places. If they cannot find a suitable home, they will often use a special ability of theirs, a tiny, supercompacting black hole they can summon with their maw, to mine out rocks to suit their needs and create a cave for themselves. They will then fill this cave with glowing crystals in any shape or form they desire, by slathering their saliva and using some unknown form of magic to will the crystals to form from it. Every Oss home has a clear pond in it. Some will consume and convert plant seeds from the surface into strange, glowing plant life from their mysterious homeworld, and grow it in their caves. An example of their environment can be found here.
Oss are incredibly food-driven creatures that love to eat. They do not need to eat, as they are immortal and self-sustaining, and made up of matter that does not exist in any universe, but they do it for pleasure and fun.

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BIOLOGY/ABILITIES

Oss biology is extremely malleable, and even capable of mild shapeshifting, and is not to be taken as unchangeable fact. Oss have long, slithery tongues with no known limit on length. The stomach is stretchy, but often tight, and the walls are lined with large, squish villi with glowing tips. They seem to have full control over their stomachs and digesting food within them, and can even reach inside as if their body is incorporeal if they please. Oss do not have lungs or basic survival organs, as they are unnecessary. An Oss' brain is incomprehensible by 3-dimensional minds, but they have one. We think.
Oss can come in any size or shape, if it is close enough to their original form. As small as a mouse or tall as a skyscraper.
As for abilities, the Oss can travel between any dimensional plane or universe they please, and are not bound by physics or logic. As mentioned before, they can summon a miniature black hole that consumes only what enters it using their maw, and are capable of manipulating the world or universe to their will. Their saliva can be willed into crystals on any surface, and they can convert one type of matter into another almost effortlessly. Oss are considered beyond sentient, but seem to enjoy acting and speaking on a level with non-ascendant beings more often than not.

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LORE

Very little is known about Oss history and origin. There is the vague understanding of a world in the Void where they originate from, but nothing is known beyond that. As for historical figures, Cheddar of the Gensis is known as the very first Oss, the original one ever created. She is the example used above. The history is so vague, in fact, that just about any past or origin story can work.

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FINAL NOTES

This species is open! Take this information, have fun with it, make your own creatures. Slap some bone plates here or there, move fur around, give them spikes if you want. This species is meant to be highly customizable. As an added note, something fun I do is I name all my Oss characters after cheeses, for a fun little secret reason. I encourage you to get silly with the names and use themes. If the species, and especially Cheddar, reminds you of something, that's because she was greatly inspired by Riven of a Thousand Voices. I thought there weren't enough bone-faced lizards around, so I made my own. Go forth, friends, and create as you please! The one depicted is simply the most basic, original form of Oss. You can deviate from it as much as you please. It's just an example to showcase the various elements of them.