It’s strange that you can patent gameplay mechanics. After all, gameplay mechanics are what define a genre. It’s like in literature if someone could patent the idea of a detective investigating a murder. How could the "pokemon-like" genre even exist if you couldn’t create a game that uses “summoning and battling characters”? Even worse, that description alone applies to multiple genres... JRPGs, or even fighting game…
You can't, with board games. I'm not sure why you can with video games. (maybe it's one of those things where you "can't" but actually you can, if you have enough money to keep anyone from successfully challenging it because they can't afford to)
Like how you "can't" patent stuff with prior art but then, somehow, big companies seem to be granted patents for things with plenty of prior art all the time?