I'm unsure whether Project Lawful's "realityfluid" concept (mostly in "the meeting of their minds", partly in "null action iii") is meant just as a storytelling conceit or as something that purportedly applies to reality.
I'll pay M$500 for a well-cited, unambiguous answer (e.g. a link to Eliezer saying "nah, it's totally just a storytelling thing"), and less for fuzzier info.
1,000I think "amount of realityfluid" of something roughly means - in how many worlds, or what fraction of all the worlds (per the many worlds interpretation) is the thing present. (Don't ask me technical questions, not qualified to explain.) And my impression is that Eliezer takes it between mostly and totally seriously. The closest I found to him defining it: https://www.lesswrong.com/posts/cfZ8zveqrTZbQrjeD/for-the-people-who-are-still-alive?commentId=umtkqgC8xHCxAtpQz see the whole post https://www.lesswrong.com/posts/cfZ8zveqrTZbQrjeD/for-the-people-who-are-still-alive for more context.
Example of him bringing up the "magical realityfluid" in a serious context: https://twitter.com/ESYudkowsky/status/1271627581704429574?lang=en