Kirby: Would probably be banned for just posting gibberish (because I assume he can't type properly).
King Dedede: We already know this because he's already here.
Meta Knight: Would probably talk about how powerful he is and that he's got his own army. And would probably become an admin.
Bandana Waddle Dee: He'd probably be confused when everyone talks about Kirby Lore.
Marx: He'd get banned for posting terrible jokes and going to his article and editing it saying that "he's the best" or something like that.
Rick & Kine & Coo: Kine is a fish, so he'd never be able to type anything. Coo would probably be so happy because most of everyone thinks he's the best Animal Friend. Rick would keep on posting Rickrolls but would always fail.
Gooey: He'd be banned for posting gibberish like Kirby.
Adeleine: Probably post her art (what else?).
Ribbon: Would talk about how great Kirby is and how much she hates ChuChu.
Daroach: He'd try to ask everyone how much money they have and then he'd get banned for asking too many private details.
Dark Meta Knight: Banned for being too violent. Threatening other users, showing pictures of the victims he killed, posting videos of him torturing Shadow Kirby (poor puffball needs more respect), etc. Though knowing him, he'd probably come back with alternate accounts, same goes for Marx and Daroach.
Taranza: Poor spider boi would get sad everytime someone mentions "Sectonia" and would talk about why it was his fault that Sectonia is dead. Though if someone explained the Lore of Kirby to him, and that Dark Meta Knight corrupted Sectonia. He'd probably wanna kill Dark Meta Knight (I assume that Taranza doesn't know the truth that Dark Meta Knight corrupted Sectonia).
Magolor: Steal everyone's Gem Apples. Talk about the ancients (he'd probably be good with Kirby Lore). He'd probably go to his article and replace all the content with a sentence saying "Magolor is the best". And he'd probably get banned for vandalism. He'd also get angry at everyone who calls him "an egg".
Susie: Would probably not want to talk to anyone. Just edit the wiki a lot, and would probably get admin. She'd probably get mad at those who hate her.
Francisca: Would probably just talk about random stuff, I have no idea.
Flamberge: Would probably get banned for getting into constant arguments.
Zan Partizanne: Would probably keep on apologizing for Flamberge's behavior. And other random stuff.
Hyness: He'd get mad at all the squidward memes about him and would go crazy like he did in Star Allies.