Zero-Two

Dark Matter was a rather strange fight, considering how much the boss contrasted with all the brightness and cheerful nature of the Kirby series.
In Dreamland 3, though, Dark Matter became 0, a giant round eye creature, which isn't much different. The thing was, 0 had a rather disturbing attack method, in which it'd open slits in it's skin and fires BLOOD at Kirby. Once you kill it, the white portion of it's body explodes bloodily, and the actual eye tries to fly into Kirby, bleeding every time you whack it. Then it explodes bloodily. It's not as violent as I'm making it sound, and you'd probably say I was overreacting. Maybe. But still, this is a Nintendo game. A KIRBY game. It's a bloodier series than Zelda after ONE boss fight.
Then...there's Zero-Two. Zero-Two lulls you into a false sense of security be appearing as an angelic being. Then it starts shooting more blood at you. Granted, the bandage on it's noggin and the suspicious green gas it ejects from it's tail in a feeble attempt to defend itself kind of makes it less disturbing, but seriously...