In particular, Trademark law that allows Nintendo to protect their brand and image.

If you haven't noticed, Nintendo's brands (Mario, Zelda, Pokemon...) are its most powerful asset. People are not allowed to make money off of other people's brands. And that is a good thing.

It goes beyond just "copyright" law, but towards "Trademark" law as well. Protecting your brand image is the absolute cornerstone of relationship building between a company and their customers.

And furthermore they've always been unusually aggressive in protecting what they perceive/claim to be their IP rights. They tried to sue rentals stores and Game Genies out of existence even before the Super Nintendo was a thing.