No you can anything and don’t have to collaborate with the artist.
You just HAVE TO ask if you can make anything inspired by it.
You can absolutely twist the ideas of the original idea of the famicase, you can have your own artstyle, different setting or original game mechanic.
But you will probably take some elements like the game idea or I often took a very similar artstyle so it’s polite to ask if you can use it.