Sigil

Sigils are a barely-classifiable species belonging exclusively to Omega Dimensions.

Appearance
Sigils are highly unusual creatures, not animal or mineral but a strange hybrid of both and yet none of them at the same time.

Visually, they are jet-black, and look like geometric shapes in a somewhat humanoid shape, including growths that look, and to a certain extent function, like clothing. They stand around 10 feet tall, but look a little taller as they usually hover off the ground. All have sharp fangs, and their mouth interiors and blood reflect their home dimensions, the exact details of which depend on the Sigil's home dimension.

However, many of the similarities end there. All Sigils have at least one pair of arms, but can have a few more, and often have one to three eyes. All of them reflect a light that does not match any existing light source, and never reflect any light around them, making them appear backlit by a certain coloured light - the colour is dependent on the Sigil in question.

Biology
Sigils have no real identifiable biological traits - they do not need to breathe, eat, sleep, or drink, and can survive in extreme vacuum and extreme pressure - they are known to be one of the only species that could survive being sucked into a black hole, as well as a total dimensional collapse.

Weirdly, they do seem to have blood, though this is more some kind of fluid that serves no real function as many of their parts are not connected to anything more than an atom in size, and the blood is more a reflective pool of liquid that soon dissipates. While it has no apparent function, the spilling of this fluid does seem to cause similar effects to blood loss, and the mere sight of it causes most Sigils to fall into a pit of blind panic.

Sigils do not reproduce. While it is theorised that Sigils may have functioning genetalia, no individual has ever found out, and Sigils are characteristically asexual, the very concept of reproduction or even sexual pleasure alien to them.

Whatever the Sigil's physical form is made of, it exists only because the Sigil believes it should exist - Sigils and related Shards dissipate upon death, and dimensional instability within an unknown range, even if it's unrelated, often calms. This crystal-like substance is also psychoreceptive, reacting both to the Sigil's and any being it encounters' minds - high-willed people are somehow able to cause more damage to a Sigil than most others, and Sigils are both incredibly hostile to and terrified of them.

Sigils also display incredible powers, mostly dimensional travel, instant transmission, the ability to duplicate and corrupt powers, and nigh-omnicience.

Shards
Sigils can also create smaller vassals, known as Shards. They take on similar traits to their creator, but are more simple in design, and often have one or two abilities at the exclusion of all others. Shards have a limited independence - they seemingly act on their own will, but their decision-making and many other senses and mental faculties are entirely slaved to the Sigil who created them. As Sigils cannot perceive everything around them until they've sensed it in person, Shards often act as scouts and vanguards for them, taking in information and probing for weaknesses.

Shards are considerably different from Sigils in terms of how they react to attackers - while Sigils physically get weaker when around strong-willed enemies, Shards do not, and are in fact entirely fearless, but this is countered by the fact that they are, relatively, much weaker than Sigils. Shards are also not created equally, and some Shards are weaker than others. The weakest ones are often sent first, as even a weak Shard is quite a challenge for unprepared opponents.

Society
Sigils are highly individualistic, and cannot withstand the presence of another Sigil in any dimension they're in, let alone within line of sight. However, they are psychically connected to every other Sigil in existence, and can tell what is happening to them within their immediate vicinity, as well as their exact Multiversal position. Most importantly, they can tell when one of them dies. However, this has no kind of hostility behind it - Sigils will never attack each other, and any attempts to persuade them either through dialogue or metaphysical means to do so will instantly and invariably fail. If two Sigils are forced into the same dimension, the one who turned up later, even if it's by an incalculable amount, will leave at the earliest convenience. On the rare moment two Sigils to decide to actually interact, they speak formally and with little to no venom.

If a Sigil ends up dying, all other remaining Sigils do not attempt to avenge their fallen kin, and in fact blacklist that dimension. After all, if one of them got killed, they're likely to get killed too.

Notable Appearances
As only ninety-nine of them exist, all the Sigils are listed below, including predominate colour.

It should also be noted that no Sigil is inherently more powerful for any logical reason - the higher number or having more lines in their icon than another Sigil does not make them more powerful, nor does any particular colour. Even if there was a hierarchy pattern, the Sigils wouldn't follow it.

Trivia

 * The very first draft of a Sigil was inspired by Bill Cipher of Gravity Falls, in terms of personality and general manipulation of things, but in a humanoid body.