You can't copyright game mechanics in the United States as they are public domain. The US Copyright Office has weighed in with:
This has been upheld in DaVinci Editrice S.R.L., Plaintiff, v. ZiKo Games, LLC, et al., Defendants. in 2016.Copyright does not protect the idea for a game, its name or title, or the method or methods for playing it. Nor does copyright protect any idea, system, method, device, or trademark material involved in developing, merchandising, or playing a game. Once a game has been made public, nothing in the copyright law prevents others from developing another game based on similar principles. Copyright protects only the particular manner of an author's expression in literary, artistic, or musical form.
Source
All the copyright covers is the exact expression used in a rulebook. Rewrite the rules, present them in a new look, etc.. There isn't a thing that any company can do to you.
What the OGL does is enable companies to use copyright misuse and to lock you out of what you rightfully can use. It is also a marketing tool to sell their books and give them a slice of your profits using illegal means. The OGL does not grant you the ability to use their logos or trademarks to market your own stuff. That's the only they can license to you.
