Let's say I want to make a version of Super Mario, not a ripoff (like super cat bros or so) but with the actual nes sprites, names and everything.
Could you please explain me the constraints and consecuenses?
Are you asking about what itch.io would do, or what legal consequences there would be in general?
itch.io terms of service forbid copyright infringement. That being said, we don't actively seek out copyright infringement in order to be included in the safe harbor for DMCA. If we're aware of the infringement though, we'll take down your content. (e.g. you admit to doing it in this post)
itch.io aside, you can be held responsible legally. If the copyright holder becomes aware of the abuse they'll typically send a takedown notice to get the content removed. It's their responsibility to protect their copyrights and trademarks. Additionally, they may opt to file a law suit against you for damages if they feel like the infringing work had a negative impact on their business.
Note, I am not a lawyer, so if you want real legal advice go talk to a lawyer!