Game mechanics haven't been copyrighted, but they have been patented.

The developers of shadow of war has a patent on their nemesis system. It's not just an implementation detail, it's the entire concept.

https://www.ign.com/articles/wb-games-nemesis-system-patent-...

>The patent protects the "Nemesis characters, nemesis forts, social vendettas and followers in computer games."

>This encompasses a hierarchy of procedurally-generated NPCs that interact with and remember the player's actions. The patent also covers changes to the NPCs' positions in the hierarchy, as well as their appearance and behaviour, again based on the actions of the player.