You are playing a children's card game about monsters. The fate of the universe is in the balance, somehow. The rules are...fuzzy. Use a standard deck. Start with 5 cards. Draw 1 each turn. Hearts are Monsters. Spades are Traps. Clubs are Magic. Diamonds are Wild. Write the following rules on a sheet: 0. You may only summon one monster a turn. 0. Monsters attack once a turn. 0. Traps must be played facedown and triggered later 0. Magic and traps don't do anything 0. You must play cards for things to happen. When you play a card explain what it is. You may, at any time, overwrite a rule or introduce a new one. Write it on the sheet and put a number one greater than the previous rule. Roll d6 equal to that number. If you don't roll any ones, all good. If you do, your opponent can immediately react to negate your action. Monster face cards have special abilities. Make them up when relevant. Other face cards remove one d6 from a roll to introduce new rules (minimum of one). Aces always roll one d6 to introduce new rules. Play until you decide it's getting old.
Thanks to those who inspired me to try this. Wanted to recreate the collaborative/competitive storytelling battle that is Duel Monsters in the first season of Yu-Gi-Oh before they decided to even pretend to comprehend the rules of the game.