THE ZERO THEORYI know that everyone is always like, 'Zero/Zero 2 i the big baddie in the series!' Well, i beg to differ. The truth is that Zero is NOT the mastermind, but only a mindless puppet of Dark Matter, the one who created it. This is why I think that:
So, in Dreamland 2, Kirby is attacked by Dark Matter, and in Dreamland 3, is working with Gooey to defeat Dark Matter. The thing is, at the time they were the only 2 Dark Matter, the one in the official artwork of DL2 has purple spheres in the back, and the one for DL3 has orange ones. So, when Dark Matter purple attacked and failed, the orange one, knowing now that Kirby could defeat him, began training, and created Zero.
So, when Kirby challenged Dark Matter, and won, DM's conscience possesed Zero like he possesed the others and attacked Kirby. But, since DM thought he would win, he created Zero with minor offensive skills. So, as a last ditch attempt, he spawned mini-dark matters to respawn somewhere else. And, when it became clear he would lose, he made the eye burst out and attack, failing, but making it away alive.
So, in the events of Kirby 64, Dark Matter escaped after combining the mini DM's to regenerate, found the carcass of Zero after the final battle of DL3, and fled to create Zero 2, this time with stronger abilities (explosive shots from its eye), and a more well hidden weak point, but still lost.
So, that's my theory! It may not be perfect, but what the heck.