Even if it were legal, it would not necessarily be ethical. People incorrectly assume that when something is ubiquitous, it should belong to the public.

Super Mario is not something that has always existed or would eventually exist, it is a creative work that became successful through Nintendo's efforts. There is nothing wrong with Nintendo wanting to reserve their rights to it.

That is not to say that Mario fan works are not enjoyable - there are awesome Mario ROM hacks and Flash animations out there - but that people shouldn't feel entitled to the rights to make them and to complain when Nintendo takes legal action.

Including the IP of the "mario" character?

I can't answer that, but my above point is the premise of the linked article.

Nintendo is reaching disney-level reliance on their cartoon hero, (probably worse) so I wouldn't be surprised to see them becoming another copyright-extending villain over the coming decades as they struggle to survive with their seeming lack of creativity.

Art yes, name probably not. I believe the name would be covered by trademark. Trademark allows for indefinite ownership.

Can you really trademark a name such as Mario?

Sure, Apple has trademarked Apple. MS has trademarked Windows. Why not Mario? It would have to be limited in use to video games, electronic entertainment, or whatever the narrowest category for such things there is.

In the context of a video game character who happens to be a plumber from Brooklyn, yes.

And movie... or are we trying to forget that that was ever made?

Hoskins must have some plumbing fetish.

What about "maroi"?