Two year ago in 2014, the creators of Bang! filed a lawsuit against the creator and distributors of the game Legends of the Three Kingdoms, claiming copyright infringement. The reason for this claim was because the Legends of the Three Kingdoms game, aside from different art, was a carbon copy of the game Bang! and so the creators figured they could stop them under copyright law. Unfortunately due to how copyright law is worded, the art of a game could be copyrighted, but the mechanisms within the game for how to play it can’t be, as quoted from the case;
In no case does copyright protection for an original work of authorship extend to any idea, procedure, process, system, method of operation, concept, principle, or discovery, regardless of the form in which it is described, explained, illustrated, or embodied in such work.
You can read more about the case, including a bit of analysis and how this might affect other cases on Zach Strebeck’s website.