2014's excellent Shadow of Mordor introduced players to a whole new Middle Earth-based story as well as the Nemesis System.
Easily the highlight of the title, it created emergent gameplay opportunities by having enemies react to your successes (and failures) in combat.
The system was so well regarded that many were surprised that it didn't make its way into other titles (other than Shadow of War, the game's sequel) – and now we know why.
Shadow of Mordor's Nemesis System Is Patented By Warner
As noted in a new Game Maker's Toolkit video (as spotted by PSU), Warner actually has a patent on the mechanic.
Check out the video below:
The way characters remember player actions may not make its way into any other titles simply because WB Interactive owns the rights.
Plenty of other mechanics have been patented. BioWare's dialogue wheel and Rockstar's AI navigation are two, as noted by RPS.
One can dream, of course.
At the time of writing, we don't know what Monolith Productions is working on – so maybe we'll get to experience it in some capacity with whatever comes next.