If you use PROP to set a thing's type to a value above 186, it creates some weird magenta material without a name. It seems to have no melting point, deforms under pressure similar to GOO, can be infected by VIRS, and can't be duplicated by CLNE or CONV. It is dissolved by acid rapidly, and isn't flammable. I can't find anything about it on the wiki, but I think that it's a placeholder for modded elements with IDs above 186. You can't save the material in an online save or stamp. I think it can only be made on mobile.
It also seems to appear in jacob1's mod but not vanilla TPT
May be partially solved: https://powdertoy.co.uk/Discussions/Thread/View.html?Thread=24092
It's just nothing. All it's trying to do is to create something from the database, but there's just blank.
However, I feel like this forum page should still be up, jacob should fix this glitch, he hasn't fixed it since he said he would fix it at April 16th.
I tried it. It didn't deformed under pressure. When I poured some powder on it, it lifted upwards (similarly to wood when it affected with neutrons). Affected by mercury the same way.
Look at my post titled "Bugged element" or something like that for more information.
Plus, look at the save titled "What?".