Zero comes from nowhere or more exactly, is the 'nothing' that everything comes from. It's the sentient embodiment of the primordial darkness that existed before the universe and will exist after it. Of course, the problem is that Zero consider everything not itself to be abherations that must be either be assimilated or destroyed. And considering Kirby booted the Dark Matter sent to take over Pop Star and begin its terraforming in Dreamland 2, Zero has kind of a very deep hatred feeding her ongoing grudge with Kirby. Almost every point about Zero and her various forms (especially the earlier ones) drips with symbolism. More importantly, she is emblematic and and the perfect foil for Kirby ; while Kirby embody optimism, hope, and a lighthearted take on the world, Zero embody fatalism, nihilism, and a surreal, dystopic view of the world. This is also shown in how they affect the setting, Kirby bringing smiles, rainbows, and color wherever he goes, Zero stripping the landscape to the shape of desolate, hellish, even lovecraftian at times realms.
The Dark Matter are an ancient species that were created by Zero to carry her will (the annihilation of reality). They are extremely advanced and infest most of known space, with only a few pockets of resistance (Pop Star in particular) here and there. Despite being created by a being of the purest evil, Dark Matters are actually misunderstood and very pitiable ; most Dark Matters are stripped of the very ability to feel positive by Zero, turning them into pathetic, insane shells incapable of doing anything else but lashing at others. Dark Matter from Dreamland 2 & 3 and the final enemy in Return in Dreamland are such pitiable beings. Gooey in Dreamland 3 is also the proof that the Dark Matters are not inherently evil ; freed from his connection to Zero, Gooey live in peace on Pop Star and is actually Kirby's best friend.
Zero and the Dark Matters have a hand, either direct or indirect in the vast majority of the serie's history.
I find it really too bad that the anime lack Zero and her goons ; the extreme contrast between Kirby's and Pop Star's happy and brightly colored world with the dreary, monstrous forms of Zero and her minions are basically a serie's trademark. Nightmare and the Demon Beasts are... a bit too cartoony and unimpressive in comparison.
(but then, I have a lot of problems with the anime, which I won't bring up further.)
On the pic... very nice perspective. Background is simplistic but works. Noticed however that you gave Kirby the Star Rod instead of the Crystal Sword though ; Kirby only took the Star Rod to fight Nightmare and considering that some games imply he keep his Legendary Weapons between games (or at least, kept one of them), one would think he'd instead bring the Love Love Stick to this fight (the Dreamland 3 weapon).
Also noticed you put the band-aid on Zero. Most people tend not to draw it as it appears goofy... though in a way, there is a reason it's there (the band-aid cover the spot where Zero's eye was ejected from its orbit when she was defeated at the end of Dreamland 3).
I'd try to come up with an actual point to give advice upon but frankly, the pic is pretty good as is and apart from nitpicks, I don't have much.
Oh my god that was incredibly interesting. I had a faint idea but this blew me out of the water. Zero's depth is way deeper than I had thought, thanks for letting me know and typing all of that up! Especially that point about Gooey, that went over my head. Do you mind if I correct myself with this description? I'd credit you of course, I love this bit you wrote.
Anyway, I originally had Kirby holding the Crystal Sword being carried by Ribbon. But as the drawing became closer to being done I tried taking Ribbon away and decided I liked the major contrast solely based around Kirby and Zero alone. And since I took Ribbon away I gave Kirby the Star Rod as well since it had a warmer color scheme and I could work with it more to establish a small glimmer of hope. The Crystal Sword could have a shine too but it seemed more glamorous than full of hope. I could have done that with the Love Love Stick but I honestly forgot about it.