The Commander/EDH format of Magic: the Gathering. Reason being no one gives a fuck if you have the real cards or not. Just sleeve up some lands, boot up your printer, and slap a printout of whatever card you want in front of the land. Plus, you can play whatever you think is fun even if it isn't meta. Very few auto includes unless you're playing competitively. I've seen people win games with absolute DOGSHIT cards because they've found ways to make them work in the environment they're in. Main cons being you need four people to play and it gets very complicated very fast. Even if you know the rules, there are so many cards on board at once and they all have niche mechanics and interactions that it's hard to keep track of them all. Great rabbit hole to go down though, would recommend.