Per 
Inter-Reality Substance.
Note: This is only a concept for an SCP idea I have. I'm currently creating jigsaw pieces, and once I have a good collection of concepts for the SCP I will proceed to format it and make it more formal.
What is it?
A substance that changes both it's physical form and properties depending on who is observing the substance. Different people observing the substance experience different properties. Any properties that the perceived substance may have only effects the subject if they have visual contact with the substance.
If multiple subjects are observing the substance then multiple properties may be observed, with substances composed of less-stable molecular structures taking priority.
For example: If one person observes the substance to be water while another observes the substance to be stone, then the person observing the stone will see the stone flowing the same as water would. The stone is not molten, however, and can be interacted with safely.
The molecular state of the substance is different depending on the different molecular states observed by different subjects. Should the two substances observed be of similar molecular structure, the end result will be equal to the less stable of the two. Should the two substances be of vastly different molecular structures, then the end result will inherit properties from both states.
One other observation is that in the aforementioned stone/water situation, only the person perceiving the water may interact with it as such. The subject perceiving the stone will find it solid to the touch, and will even find themselves being pushed away if the water flows in a way that would normally encase the subject's hand.
The substance appears to go through a “transition period” every 24 hours, with observers reporting that the object seems to 'fade' between states. One important thing to note is that if multiple people are observing this substance when this transition occurs, the substance will take on the exact same properties for all personnel present.
The substance does not appear to interact with any inanimate objects in the way it is expected to. Should a person perceive the substance as something at dangerously high temperatures, the substance will still cause burns on the subject but will not effect the subject's clothing.
The substance appears as a pure black substance to any and all recording equipment, and it has been observed that recording equipment set to observe the substance for a long period of time will eventually overheat and stop working.
Location of origin:
The substance was discovered in a lab in <insert location here> contained within an air-tight container with a viewing port.
//Could possibly have the substance interact with inanimate objects, with the initial container being somehow inert.
Possible combinations of interest:
Molten rock (Subject 1) + Helium gas (Subject 2) :
Resulting molecular state: Gaseous
Subject 1 and subject 2 were stationed in an observation chamber.
Subject 2 perceived an empty chamber.
Subject 1 perceived a room with a glowing red gaseous substance collecting at the top of the chamber.
Subject 1 reported that the substance was giving off an intense heat and requested to leave the room.
Diamond (Subject 1) + Clear liquid (Subject 2):
Resulting molecular state: A previously unknown state. Appears to be a liquid consisting of an ever-changing crystal lattice.
Subject 1 permitted to interact with the substance, attempts to push their hand into the substance. Is unable to and can interact with the substance as if it was solid.
//Possible footnote #1:
Note:
The existence of this material suggests that each person is living in their own reality, with each person's reality governed by a central set of rules that are exactly the same in each reality - not unlike a set of clients connected to a central server.
My theory behind this substance is that the laboratory somehow managed to de-synchronise the substance within this central 'server', and therefore each 'client' is not sure what the substance is supposed to be.
It appears as though the transition period is the substance's attempt to re-synchronize itself with each 'client'. Why the substance is unable to communicate with the 'server' and automatically synchronize itself with each 'client' is unknown, perhaps the scientists managed to sever it's connection in some way. The search for equipment displaying possible anomalous properties within the laboratory is currently under way. - Dr Graham
//Possible footnote #2:
Note:
This shit's part of the Matrix, yo.
