@simone54 Plenty of copyright violations never get prosecuted. That doesn’t mean they aren’t violations. Not all companies are equally diligent in protecting their copyrights. Disney is extremely aggressive, for example, whereas Nintendo is fairly selective. Abobo’s Big Adventure has two things in its favor: it has a prima facie defense posted on the website, and the game is probably doing nothing to hurt Nintendo Co., Ltd.
Copyright holders tend to be primarily concerned with two things: keeping their copyrights intact, and not losing revenue due to infringement. The first is a major driver of copyright lawsuits. If Disney turns a blind eye to someone’s use of Mickey Mouse, they could wind up losing their copyright for failure to enforce it. This gives them a reason to care about the infringement even if they otherwise would not.
The second also drives lawsuits, but not as many as you might think (though the RIAA MPAA are doing their best to change this trend). This is why putting up a prima facie defense is good cover. Nintendo can’t lose its copyrights over a parody because parodies are allowed exceptions. Leaving parodies alone does not count as failure to enforce. And since Abobo’s Big Adventure also does not hurt Nintendo’s bottom line, the company has no real reason to bother sending a cease and desist.
It could still happen. Some people just don’t like to see “their art” being used by others and will use any pretext to prevent it. Like I said above, though, the main reasons that people file this kind of lawsuit are to protect their copyrights and to prevent the market for their work from shrinking. If a copyright holder does not think you are doing either of these things, you are often—but not always—safe from anything more than a takedown notice.