I really don't have a clue. Why was the question put on hold as too story-based of all reasons?
This is a blunt response
1) You can't ask a straight question.
Your entire question could have been asked as follows:
creature-design I am designing a creature with a body made out of a fluid similar to a magnetorheological fluid, save that rather than using magnetism I'm using nanomachines. This allows the fluid to become a permeable solid not unlike the holographic doctor in Star Trek: Voyager. What would be a good fluid to use as the suspension for the nanites?
- It must be magnetically permeable.
- It should have good cohesion.
- It must be fireproof and resistant to acids and bases.
- It should be lightweight
We don't usually mind creativity in the questions, but it should never interfere with your question being concise and clear. As the quantity of flourish increases, the comprehensibility of your question decreases. For example, your Objective #2 required me to read it a couple of times to realize you were trying to be funny and not actually trying to add anything principally meaningful to the question.
(BTW, IMO you should replace #2, which is irrelevant since your nanites are creating the cohesion, with a minimum temperature the fluid must remain a fluid. As temperature drops, everything eventually solidifies. You might also consider a maximum temperature for your fluids, as some materials won't be fluid at your max temp.)
2) You asked about one character.
How you ask a question is important on this site. We aren't being rude, we're trying to draw a clear line. The moment you made this about a single character you made this too story-based. Single-character questions are
almost always closed because a single character is 100% a function of the story — he/she/it can literally be whatever you want them to be because there's no reason for consistency (which is required for even a second creature of the same type).
3) You're asking a question about magic.
Your knee-jerk reaction to that statement will be, "no I didn't!" But yes, you did. Nanites or nanomachines fall squarely inside Clarke's third law:
Any sufficiently advanced technology is indistinguishable from magic.
This means you could use urine (or any other non-solid) and achieve what you want. Just have the nanites solve the problem, which is a story-based solution.
Asked in a better way this question might have been popular
I believe if you fixed (1) and (2) then ignored (3) the question would be reopened and might even become quite popular. It's an interesting question. There was just too much nonsense to wade through.
One more thing: it's important to keep in mind that the longer your question, the more likely people will skip it. Many users are squeezing in a free minute here and there to participate. They won't/can't take the time to read a long question no matter how relevant the marshes. And when they realize the marshes aren't relevant, they'll tolerate the question length even less.