Share your own game rules you have made up that are not the way the game was originally meant to be played.
One that I remember is in “Monster Jam” for the Nintendo Wii, there is no free roam but you can play a “destruction mode” that has a time limit but works good enough. There is a map where you can go up on a roof and the goal is to push the other ones down being the last one standing when the time hits 0. That’s it. It was inspired by an flash game with the title “one must fall” I believe.
We played this a lot. Its funny how you only need a “interesting” physics engine for a game to be fun.
In GTA 5, get on a train, get a wanted level, try to keep the wanted level for an entire round-trip around the map, then try to escape the wanted level, all while staying on the train and surviving.
(it’s been a few years since I tried this and don’t remember if those were the exact rules, but they were something like this)
Me and my mates would get on the train together on online, put max bounties on each other and try to take on the entire lobby.