A mysterious chemical, it cannot be synthesized naturally by any means at all, you can only get it through Noah, only if he allows you to use it will you be able to.
The chemical's properties are in constant change as the chemical is not suppose to exist and knows it, constantly shifting to fit in, allowing it to be shaped into virtually anything as long as it allows you to wield it.
As for using it, it is primarily used to counter nightmare's power, due to the nature of the chemical and nightmare's body constantly shifting to stay together as he should also not exist, they can match together in sorts and be twisted to cause major damage, the Basis of the Magic nightmare uses is chaotic in nature as is the basis of this chemical, if you know how to use it and can, you can shred through those who oppose you, nightmare is physically better in defense so it would take a lot of it to kill him as he could shift his magic to regeneration or just flee, it of course can be used as a solid material for building and other uses though that is ill-advised as due to the chaotic nature of the chemical, one property of it that is constant is it is highly unstable
How unstable...well it depends on the tier of its power, the chemical can be combined through careful atomic level modification with itself to become stronger but the unstable nature greatly increases every time this is done, due to the very small amounts your modifying for a tier 2 chemical, it will not cause much damage, you will most certainly need a new lab and some body parts though, going for a tier 3 causes such a major boost in how unstable it is and due to how much it requires to stay within a realm of stable that trying to go above tier 3 is highly dangerous
The chemical used as a basis for bombs though, especially with radiation makes it so much more unstable, that in any case using it for a nuke like bomb is deemed a breach of international security due to Noah's interference to greatly limit the use of the chemical expect by him as he is one of the few that would easily be able to wield it...But if that was not the case, the use of a chemical N nuke would cause more damage than the strongest of nukes man has created, along with tearing holes in the space time continuum which tends to be highly unstable anywhere nightmare and noah meet
As for obtaining the chemical, only Noah can create the chemical through his reality wrapping capabilities but will only allow it to be used directly against nightmare, it can only be wielded at the most basic level which is very weak unless you meet three conditions, or if Noah disables it for you, he has only trusted some variations of Chara and Frisk to use it under certain circumstances
1 - you must have determination, before you say all humans have some determination, it must be more than usual but does not need to be a soul of determination, the most likely otherwise soul types to use it would be Justice and Bravery (due to the connection to nightmare) as they would have determination if they are actually going to attempt to fight nightmare
2 - You Have a VERY VALID reason to use it, most often as to fight nightmare or anything using his power to sustain itself when it should not be there, such as anomalies in space time, for instance nightmare granting Jeff the killer or someone power to traverse into another universe as to cause harm, they would in that case be wielding some of his power, therefore also giving a weakness to the chemical until they screw off with nightmare
3 - You have permission from Noah, noah is the master bender of the chemical and has the most control over it, he will only let you use it if you meet the following two requirements as having a soul that can handle it and a Valid reason, as well as being judged by him to be safe to use it under a certain situation, however once the task is done you will lose your power over the chemical
As for appearance, it can take any color, though typically mimics the color off the soul of the user, for instance a user with a soul of justice (Noah) would make it yellow, or a user with a soul of determination (Frisk, Chara) would make it Red, and so on for the rest of the souls, if a non human or humanoid creature uses it, the color it takes can vary but most often white, anytime nightmare tries to use it turns it black and it then sorta just tries to kill him
If nightmare were to ever take control of the chemical, it would mean disaster for everyone, due to nightmares plots weakening space and time, Noah has turned to using it as a sorta oxygen throughout space and time as to help support it, due to Noah controlling it, if nightmare were to kill him, he would gain control of the chemical for a few moments before it recognizes who he is and then would try to kill him, but without Noah controlling it, it would do whatever it takes to kill him, under this situation it would kill everyone if that was what it would take to kill nightmare, as the chemical does not have a system of emotions to make it feel guilt for killing more people than every genocide that has ever occurred