Cloning games is fraught with legal difficulty because the courts appear to consider video games as audiovisual media for copyright purposes and not strictly computer programs. This means that if you develop any game which is "substantially similar" to another game, even on a surface level, you may be found liable for copyright infringement. K.C. Munchkin shared neither code nor assets with Pac-Man, for instance, but because it centered around a "gobbler" that ate dots and avoided monsters, it was considered similar enough to Pac-Man to infringe on the latter's copyright.

Whatever you do, never ever clone Tetris. Henk Rogers has lawyered up like no other game developer has, and asserts copyright on all falling-tetromino games, as well as trademark rights on various generic elements of said games, including the shapes of the tetrominoes themselves and the public-domain song "Korobeiniki" when used in video games. If you clone Tetris without authorization from Tetris Holdings, you are at grave risk of being sued; if you are sued, you will lose.