Magic is such a weird example to use... People play their own games with it, with their own rules, literally all the time - https://en.wikipedia.org/wiki/Magic:

Magic is such a weird example to use... People play their own games with it, with their own rules, literally all the time - https://en.wikipedia.org/wiki/Magic:_The_Gathering_formats https://en.wikipedia.org/wiki/Magic:_The_Gathering_formats The above link is nowhere near close to exhaustive. Many of the formats on it were made up by fans, and then eventually made quasi "official" once a popularity threshold was reached, like Commander. In fact, the entire premise, from the get-go of Magic: The Gathering was incredibly flexible modularity. Every time you change your deck, you're 'changing the rules' of the game. It's Turing complete, and people have made some really wacky stuff with MTG cards. And, there's no small amount of proxying going on. Many, if not most Commander players allow a few proxy cards. High level tournament preparation involves 100% proxies. Online platforms allow you to play with any card in Magic's history for free, if you're willing to don the pirate hat; and if not, you can play MTGO or Arena.