Game mechanics can be patented. It's stupid, but things such as "loading screen mini games" and "overhead arrows pointing to your objective" have been patented. The second I believe even got enforced once.
I think these kind of things have been getting approved less and less, but I wouldn't be surprised if "balls that contain monsters" was patented back in the early days too.
HOLY SHIT you have no idea how long I have been trying to remember this game. A cousin showed it to me when I was young and I loved it. Next time I saw him he'd forgotten, and I never could find it when I finally got a PC!
I can't believe it's been under my nose this whole time (Paladins fan) and it makes complete sense. Thank you for unlocking a core memory 🙏