I seemed to recall such Mario clones as well. Nintendo is quite protective of their IP, so I have to think that they must have threatened legal action. Does anyone know? Is there precedent for legally protecting the layout of a level?
I think the clone I'm semi-remembering was a PC game. Regarding your second question: There were very many unlicensed Nintendo games. I don't know how many of these Nintendo fought. They very famously battled Tengen over this issue in the courts.
