Random, cause I've thinking about this off and on...
...could the Void/Nil-esque object in the background of the True Arena fight (I’d get a screencap but I’m having a lazy day...) be one of the many countless Voids said to exist? Is it in the process of being formed by this battle?
[Screenshot shamelessly grabbed from aWiibo on Youtube]
Can the crown itself not give birth to new Dark Matter (Magolor’s body being only a shell, even as “he” is locked away inside it) but the negative energy being formed from this fight (...Magolor’s weeping is a good sign this fight is producing a LOT of negative energy) enough to, well, give birth to one? Maybe Magolor could be transformed into a servant Dark Matter, like Blade, and what is going on in the background is the creation of a new “Zero?”
We see the sphere go from just an amorphous black void to gaining the Nil-esque stripes after you reach (read: divert to) the phase of the battle where everything has reached the speculated "bad end." (And remember how Dark Matter/Zero’s arrival was always the last thing to happen in the “bad ends” of the Dark Matter trilogy?) There's also the fact that it's dark blue, looking more like, say, Gooey’s colors than Void Termina's white/pink colors. (Colors associated with Kirby. Also note that Void Termina was able to be reborn/reformed) I wonder if that’s the case...
I’ve been thinking, since a lot of fans have said “what’s the point of having the last thing you unlock in the game be a “bad ending”? Isn’t that just cruel? But I’ve been thinking lately, what if it’s not solely a bad ending to make Kirby feel sad and torment Magolor, but a new ending to forge the way forward into a new arc? A sliiiight pivot away from the Ancients and the preparation for a real deep dive into the story of Dark Matter, Zero, and Void?