Mini Mao is a simple but rapidly-complicating card game for two or (ideally) more players, in which the winner of each round is allowed to add a new rule to the game. All such rules are secret, and their effects must be deduced by the other players through observation and experimentation.
Mini Mao is a cut-down version of Mao - it's a lot friendlier to new players, without losing much of the mystery, superstition, deduction or paranoia. The basic game idea is very easy to remember, and you can teach a group to play in a couple of minutes. (Concerned Mao veterans should be assured that this page does not give away any of the significant rules of Mao. I'll explain later.)
To play Mini Mao, you'll need a regular deck of poker cards. Keep the jokers in if you've got them, but it's playable without. Decks with a couple of cards missing or bent are fine.
You can also play the game with a Tarot deck, a pile of Magic the Gathering cards, some (varied) business cards, or any collection of distinct cards. If you're using something particularly unusual, agree among yourselves on a few elements of the cards which will count during the game (eg. "person's name and the first city listed, on business cards"), and which should be ignored.
To begin; shuffle the deck, and deal five cards to each player. Place the leftover cards face-down in the middle of the table - this is the draw pile.
Select a player to make up the secret rule for the first round. You can choose the person randomly, or go with the first player to think of one. (In a two player game, both players make up a secret rule.) Secret rules take the form of simple restrictions, side-effects or alterations to play.
When a secret rule has been invented, everyone picks their hands of cards up. The top card of the draw pile is flipped face-up onto the table, to form the discard pile.
Starting with the player on the rule inventor's left (or with a random player in a two-player game), players take turns one after another, proceeding clockwise, and each turn they must either:-
If a player plays a card which breaks somebody's secret rule, that rule's creator informs them that they have done so, but does not explain the rule. The offender takes back their illegal play, and draws a penalty card from the draw pile. (If they broke more than one rule at once, they should be told this, but only get one penalty card in total.) This ends their turn.
If a rule has a trigger effect (eg. "after playing a two, the next player draws 2 cards" or "after playing a four, move it to the bottom of the discard pile"), the rule creator should wait until the move is confirmed as legal under everyone else's rules, and then step in and apply or announce the effect without further explanation. (If two triggers clash, process them according to the clockwise order of their creators, from the active player.)
The first player to empty their hand wins the round. The deck is shuffled back together for a new round, and the winner gets to make up a new secret rule. This new rule operates in addition to the secret rules from all previous rounds - the game gets more and more complicated as it progresses.
The game continues until it locks up - eventually the secret rules will mesh in an unexpected way meaning that no card can be legally played on top of the discard pile, or that it is clearly impossible for any player to ever empty their hand. At this point, declare the game over.
When inventing a secret rule, keep in mind that rules are always harder to guess than you'd expect them to be. As a benchmark, something as simple as "can't play a heart onto a club" is about right to open a game with. An excessively complicated rule ("You can't play an even red card on an odd black one, unless the second-previous card was of the same suit, or the turn number is prime") won't ever be guessed, and you'll slow the game down having to carefully check every play. And a blatantly abusive rule ("The creator of this rule automatically wins every round! And everyone has to give them money!") just means that your friends won't want to play Mini Mao with you again.
It helps a lot if players come up with a piece of jargon to describe each of their rules - a verb or a noun to use when the rule is broken or invoked. ("You can't play a three, that's offside!") This is useful for clarifying which particular rule has been broken, when a player has won several rounds and has more than one rule in effect. This removes one advantage that allows leading players to get even further ahead - if I've won my second round and you haven't worked out my first rule, it's now much harder for you to deduce either of them, because you don't know which rule a given play is breaking.
Jargon is also useful for keeping the game intact - you might call a gronk by mistake, and a third player (who's also worked out what a gronk is, and doesn't think that was one) will be able to question that, rather than assuming that a different rule has been broken. Jargon can be chosen to give a hint of the clue's nature - perhaps playing face cards onto one another is "intrigue" - or can be deliberately misleading.
Jargon also impresses or confuses an external audience. An evolving Mao game is largely indistinguishable from a mysterious, elaborate card game.
Bull, Gogol and de Worms are playing a new game of Mini Mao. It has been decided that Gogol will invent the first rule. (And that whenever they speak in bold, it means they're playing a card.)
Gogol : [thinks] "Okay, I've got one."
[ Gogol flips the top card of the draw pile - it's the three of diamonds - and everyone picks up their hands. ]
De Worms : "Right. The eight of hearts."
Bull : "King of spades."
Gogol : "Five of clubs."
De Worms : "Two of diamonds."
Gogol : "Sorry, that's a Pip, you can't do that."
[ De Worms grumbles, takes back the two of diamonds, and draws a penalty card. The top card is 'five of clubs' again, and it's Bull's go. ]
Bull : [tentatively playing a card] "Is the two of clubs alright?"
Gogol : "Sorry, no."
[ Bull takes back his card and draws a penalty. ]
Gogol : [pleased] "Nine of spades."
De Worms : "Three of hearts?"
Gogol : [deciding to be generous and give de Worms a clue] "No, too low, you're Pipping again."
[ De Worms takes back the card and draws a penalty. ]
Bull : "I think I've got it. Ten of hearts?"
Gogol : "That's fine. King of hearts."
De Worms : "Eight of hearts...?"
Gogol : [silent nod]
Bull : [triumphant] "Nine of clubs!"
Gogol : [despairing at his cards] "I pass."
If your deck includes any cards which don't comfortably fit the usual criteria of other cards, you can refer to them as jokers (perhaps they are jokers) - they can be played as if they were a copy of any other card from the deck; the player calls a card when they play it. Jokers are very useful to have in the game, as they can save situations where only a handful of cards are legal plays, and may already be buried in the discard pile.
If you're playing with a poker deck, be sure to agree whether aces are high or low; ideally before the game. You can make their highness or lowness part of the secret rules ("Number cards cannot be played onto higher number cards, and aces are low for the purposes of this rule."), but it can get confusing if two rules treat them differently.
Mini Mao began when I was killing time with some friends and a deck of poker cards in 2002, and, on the subject of games with hidden rules, I vaguely recalled Mao - but only that it was a Bartok variant, with secret rules and no initial ones (not even suit progression). We played a dozen or so games of it like that, starting a new batch of rules whenever we got bored, and it worked.
Checking for "official" Mao rules online when I got back near a computer, though, I found that they were actually quite elaborate - standard Mao can be regarded as an already-begun game of Mini Mao, where the game so far has already been played for a dozen or so rounds by some Californians you don't know. It forces you to play a certain type of game, with suit progression and number-effects, and doesn't encourage restarting when the game locks.
Mini Mao is just a crystallisation of the rule-making, rule-breaking and rule-meshing aspects, putting the initial rule-maker only one rung above everyone else, and making the game a lot more personal for those playing it. It's a much kinder game to introduce to new people, particularly if you're the only one who's played it before. The world needs more games that you can explain in three minutes and play for hours, with a single deck of any old cards.