In many variants an additional rule is silently and secretly added to the game with each round. It is customary for a player (often the winner of the previous round, sometimes the next person to deal) to add one new rule to the game. In a game with only one round, players who have gotten rid of all their cards may make a rule for those still in the game.[20] Sometimes a new rule is explained to one other player (sometimes the dealer, sometimes a runner-up winner of the round), both to ensure consistency of the rule and consistency of its enforcement. Any new rules are allowed, but it must not be biased towards a player. It will be unfair for the other players and the game includes everyone.

There may also be additional rules that are already in effect at the beginning of the game, just to get things moving, and these rules may be known to all players, or perhaps only to the dealer. After many rounds, many new rules will accumulate. Naturally, only the person who created the rule will initially know what it is. The rules will vary from group to group, and from game to game, but most rules fall under one of the following four categories.[17]

When an event occurs, a player must perform an action (such as speaking a phrase or knocking on the table)
When an event occurs, something about the game changes
An action must always, or must never, be performed by players (such as holding cards in the left hand, or straightening the pile)
Something fundamental about the gameplay changes (e.g. all kings are treated as if they were jacks for all game purposes)
The triggering events in the example above can be anything. They might include playing a specific card (the ace of spades) or a specific type of card (any red three), but triggering conditions can become as complicated as their creator wishes, such as when someone plays the fourth card of the same suit or playing an odd-numbered card on top of an even-numbered card.

To create a rule, one could pick a triggering condition, and then an action and/or game effect. The spirit of the rule is generally something in good fun; while rules that unfairly sway the game in favor of one player or to the detriment of one specific player are quite easy to concoct ("Every time James plays a ten, he gets a penalty of ten cards"), they are also generally frowned upon as unsportsmanlike. Rarely do rules have a penalty of more than one card, but certain rules have a large penalty attached to them, usually the result of a cumulative