Not filler per say, it does set up a basic foundation of what you need to know about the Gu Immortal realm/world/level of cultivation. That being said, it's a fairly common bit of criticism among long-time readers that the pacing of volume 4 is, well, bad. It's easily the worst of the 5 volumes currently finished in terms of quality, and vol. 6 is also way better so far. I've heard it said that vol. 4 is the "Introduction to Gu Immortal Cultivation", but other than setting up some of the longer term plot points that don't start paying off for another 400+ chapters (in vol. 5), that's... basically all it manages to do in something like 370 chapters. When I was reading through for the first time, I found myself skimming parts of vol.4 - the only time I've skimmed any part of DG. As for the new body bit? Spoiler: Spoiler The basics of it is that Gloomy Soul (one of the 10 Venerables), as part of a... very long term scheme, attempts (and partially succeeds at) refining a Gu called the Paragon Immortal Body Gu, which, well, has a boatload of major advantages, and, due to the refining being only a partial success, a few major flaws. The function of the Paragon Immortal Body Gu is to create a 'perfect' (or 'paragon') body without a native soul, which Gloomy Soul can then possess/control by putting his soul into it. FY manages to steal it in a complicated series of events during the climax of vol. 4 - the dream realm is condensed true meaning from GS, and is used in the refinement. And yes, GS is still dead during all of this - the refinement is being done by GS's soul fragments/clones (i.e 'Shadow Sect') which he left behind after dying. Edit: Been a few months since I read these parts, and I got the part about the dream realm wrong. It wasn't used in refinement, it was the result of one of GS's clones self-destructing during the events in question.