I loved Calvin and Hobbs when I was little.
Calvinball, from Calvin and Hobbes, is a game that you just make up as you go along. The only rules are that you have to wear a mask, and you can't do the same thing as you did last time.
It goes like this. The game starts however it wants to, and then a player makes a rule. The players play through that rule. Then another player makes a rule (said rule accepting earlier rules and adding to them, or rejecting and replacing them) and the players play through. Then another player makes a rule, and on it goes.
These sequences can be overwritten by new rules, and the sequence of who gets to make what rule can go in whatever sequence the rulemakers make. Maybe somebody leaps over something, and this leap leads somebody else to make a rule about how many leaps are required or limited, and the new number of leaps changes how many balls have to be in the air between leaps or how many leaps have to happen while the balls are in the air, and eventually you’re singing “The Very Sorry Song” or asking, in verse, for Suzie to dump a bucket of water on your head.
Somebody leaps over something, and then it goes from there. It doesn’t have to happen this way, or really any way, but it’s best to start somewhere.
The only rules from Classic Calvinball seem to be that you have to wear a mask, and that no game can be played the same as last time. Masks aren’t required in New Calvinball or Calvinball Variations, and it seems unlikely that any game would repeat. But the other elements remain. Things happen, somebody makes a rule and more things happen in adherence to that rule, and somebody else makes a rule and more things happen, and on.
I sometimes think that I've been trying to play Calvinball since I was a little kid.
Especially lovely is the story arc where Calvin's game allows there to be peace between him and the babysitter.
*Also, Supreme Court Justice Kentanji Brown Jackson just referenced it in a dissent. “Calvinball has only one rule: There are no fixed rules. We seem to have two: that one, and this Administration always wins.” (She's becoming my favorite.)