Right, it's legally OK to backward engineer something. There is no copyright or legal protections on the 'how'. > but if you mimic whole bunch of specific feat

Right, it's legally OK to backward engineer something. There is no copyright or legal protections on the 'how'. > but if you mimic whole bunch of specific features, APIs or whatever, it is still tricky legally. If you mimic an API, as long as you can prove you didn't copy any of the original code or engineering - you are in the clear. > because Nintendo emulators are creating parallel market for Nintendo devices No, they are not. The parallel market only pertains to games (or specifically, the creative work that covers the IP for the game).