This is really a topic that no one here can answer for you. First, copyright rules vary from country to country. “Fair use” I don’t think would apply here. Fair use has to do with using it in educational or editorial situations. That is a college professor could take a screenshot from a game and use it in a presentation to talk about the game. That is fair use. Or if a newspaper is writing a review of your game, they could use your app icon in the review. Fair use would not apply to cloning a game.
Also, you should learn about the different intellectual property (IP) protections. Copyrights are different from Trademarks, which is different than Patents.
There is also a difference between “Illegal” and “Unethical”. There is also a difference between criminal and civil when you talk about the term “illegal”.
I think most people here would support being ethical and suggest coming up with your own ideas.
Rob