The nintendo mafia came for steam and got them to remove mods with their characters. Can they do the same for fanart? At least in the usa?

I don't think they can...

majority of fan art falls under fair use and frankly would be a shit look to the company to threaten legal action against 8 year olds drawing pikachu

look,anon..get some long rest,you look like you're living in a "rabbit hole" paranoia made specifically to mess with your head all the time..and stop fear posting about something you barely know about..case in point..nintendo is a hardline copyright zealot to some people...I don't want them to be like that everytime this needs to happen..all it needed is concrete evidence..besides,they're just regular business folks,not copyright-focused company..otherwise we won't be here today.

we all grow up playing nintendo games,buying their merch with fair economy,drawing/creating/organising fan contents somewhere..even I did it at some point,but there's no way am I gonna post it online..I don't sacrifice my hard-earned life savings just to settle some legal fee..if that's how it has to be..how will I live later on? how will you live later on?

tldr: please no more vague fear mongering,it's not for everyone

You can post online as long as you're under the radar before release.

impossible,try it on some "social media" site and see how quick it'll be taken away..you know..they're like Trunchbull from Matilda..if they see just one harmless fanart,they will alert the copyright holder and cyber-harass the poor guy to the point of having suicidal thoughts..I can't let them,no one can.
be logical,and reasonable... is it even worthy to indirectly kill an innocent over a simple fanart online?

Mario Fangames Galaxy
SMBX (which still there despite C&D)
SMWcentral
Need I say more?

The most important rule is to not make such a big deal out of it, don't announce your fan made project until it's finished. Don't promote your project via patreon and/or dare you to make money out of it. Even if they strike down, the product itself still lingers on the internet since it's impossible to remove it. Nintendo (and most companies, notably Japanese) doesn't know how the Internet works.

Yeah, with Nintendo you have to avoid doing a loud announcement. It is way worse if the game is still mid development. Cease & desist at godspeed.

these days you got thieves in the fandom masquerading as a "die-hard" fan. and most of them try to play god with nintendo..and you know the risk is a lot higher than settling a casino/essential house facility debt,it's all I could say for now,I'll try to work a follow-up when I got the chance.

Maximinimal, you really shouldn't be talking about other people being paranoid. In the past, you've flipped out over things sounding like a conspiracy theorist, LOL.

Anyway, yes Nintendo has came after lewd fan art before. There were a few artists who claimed they got a C&D before, and have since dropped doing Nintendo work. One example was a Newgrounds hentai game starring Princess Peach that was in development for years, until Nintendo came along and requested a C&D, killing the project.

Another example, although I'm not sure if I could still confirm it's veracity, was Akairiot, who did Nintendo lewds back when Super Smash Bros. for Wii U was still new (and one of my earliest favorite fan artists). He got a C&D, and started doing original characters instead. It's been so long that he actually still does Nintendo lewd art from time to time, but it's mixed in between OCs and characters from other video games and media.

I don't think they actually attempted a mass purge of that kind of content, and luckily it seems to be a rare event, but it's definitely happened in the past and it's definitely possible.