((okay so this is super-delayed and probably sounds HELLA RUDE but anyway re: thedenizensofpopstar's post concerning the similarity of Nightmare, Zero and 02's bossfights:
they are actually not similar at all. Nightmare is your classic Kirby boss fight: a platformer boss battle with your weapon of choice, in this case the Star Rod.
Zero is a side-scrolling shooter, and 02 is a 3D rail shooter. even the presence of special weapons doesn't count because the kirby series is really fond of the Eleventh Hour Superpower trope, to the point where it's used in all games bar the first and Canvas Curse. if that is what you use to draw similarities between these three boss battles, then by that logic nearly every boss in the entire series has something to do with each other - and that theory is one that the fandom like to peddle like mad with little to no basis other than "GUISE WOULDN'T IT BE COOL IF DARK MATTER WAS BEHIND EVERYTHING OMG LOL". admittedly I am ferociously biased against that theory but it has plenty of objective reasons for being false: the popularly-cited "Drawcia made a pact with 02!" explanation is completely false; to try and tie every boss to Zero/02 not only insults HAL's creativity for character-building but is also really lazy writing, and in some cases is just pure ass-pull.
Nightmare as a product of Dark Matter I could understand; the guy is a force of evil manifest and shares the apparent exclusive weakness to a "holy" item, but those are the only similarities and even those are little to base a connection on. I've seen plenty of people try to explain Marx as being a result of/influenced by Dark Matter and that's just insulting because his entire story and motivation is laid out for you and not a single mention of 02 is made. He doesn't even have any thematic or visual similarities to hide behind. Even Magolor, the current most popular "HE'S TOTALLY DARK MATTER U GUISE" has a thoroughly fleshed-out backstory with no connection to Dark Matter whatsoever. the only reason people started making that connection is because of the eye he has in second phase/soul form, and even that has a non-Dark Matter reason! it's the Master Crown's eye! you're explicitly told that Magolor soul is literally Magolor's corpse being puppeteered by the crown. as well as that, the crown is an artifact from a whole different dimension, so it seems unlikely that 02's influence would have spread that far.
the most overarching issue with the fandom's habit of associating everything with Dark Matter is that it kind of implies that no-one in the series can be evil without being forced to it/being a creature of pure evil to begin with. that's lazy writing and gets real boring after about the third flat villain. I think HAL is even aware of this and that's why they've made some characters explicitly just bad on their own without external influence. Marx was a jerk. he got the sun and moon to fight and stole Kirby's wish for the sole purpose of dicking Popstar about. Magolor was a royal douche; he pulled a Marx except better. even Sectonia was a bad person before her exposure to the mirror.
anyway, as I said above, I really hate the whole "everything/almost everything is Dark Matter" theory, because a lot of it, to my mind, stems from poor reading comprehension and willfully ignoring the canon to further one's own fan theory. I have seen this theory done well. it is just excruciatingly rare. this post turned out mad long but I guess my underlying point was: to infer that Nightmare is in cahoots with Zero/02 because of similar fights that are not in fact similar at all seems fallacious to me.
THIS IS NOT AN ATTACK AGAINST YOU PERSONALLY PLEASE DO NOT TAKE IT THAT WAY))