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How closely can a game resemble another game without legal problems
I'm going to make a game in the form of a 100% free Android phone app that will be basically a clone of an old arcade style NES game, but with a few modifications to make it better. Now the game I am inspired by was released in 1985, so I'm not exactly shitting bricks about being sued, but I just thought I'd ask on here first about what kind of legal considerations developers go through when copying others' games.