

IANAL, and this is oversimplifying. Copyright protects the creative elements of a game, including the specific way that a game is coded (so you cannot decompile a game, modify all the art assets, change the code a little, and then sell it), and possibly aspects of the gameplay required to give it a specific “feel”.
If you want a solid legal defense for cloning, you could have one team that describes the original game in a way that removes the creative elements, and a second team that works from that description to make a new work. This works for other works, too; I can write my own “book about an orphan that learns he has magical powers, goes to a school to learn to use those, and ultimately battles and defeats the powerful dark wizard that killed his parents”, but can’t sit down following the story elements of Harry Potter for my new Barry Cotter book series.
Ultimately the line is what you can convince a judge and/or jury is “different enough”.






When I was a child, my elderly neighbor grew pears, and they were the best pears. My parents live in the same house, and the pear trees my elderly neighbor grew are still in the same spot, still alive.
The pears on those trees aren’t the same anymore. They turn meally before they get soft, and they never get sweet enough. They don’t have the same strong flavor, and they don’t bake up well in desserts.
She taught me many things about growing plants, but never anything about what she did for the pear trees. So now pears aren’t what they’re supposed to be, and the reason is lost to me.