The term "exception based games" or "games with exception-based rules" is used to describe games that modify their own method of play ("ruleset"). Unlike traditional games, like Chess or Risk, in which the rules are fixed at the beginning of the game and do not change during the course of play, exception based games provide a set of options that change the operating rules, generally as a possible move.
An elegant example of a game with an exception-based rules is the card game Fluxx (Looney Labs, 1997). A class of cards in the game (called "new rule [cards]") set the number of cards that are drawn or played in a single turn. Another class of cards (called "goal [cards]") set the win condition for the game in progress. Subsequent plays of rule cards or goal cards replace the current state.
The canonical example of a game with exception-based rules is the board game Cosmic Encounters (Eon edition, 1977). In this strategy wargame, each player is (randomly) dealt an "alien power" that allows them to break a specified rule in a specified way. These exceptions impact every aspect of the game play, from card drawing to order of attack. The first revised edition (Mayfair edition, 1991) of the game came with 48 aliens, and their expansion (More Cosmic Encounters) included even more.
An implementation of this idea in the genre of abstract strategy games is the GIPF project (Kris Burm, 1997). In the primary game, GIPF, the players are allowed to challenge the other in a supplemental game (expected to be one of the other GIPF games) for an additional means to move pieces. The winner of the supplemental game gains the exception.
Many collectable card games tend to be exception based. This emphasizes the importance of the cards to the game play at a deeper level than merely using cards as a substitute for a board and pieces. However, by printing rules-exceptions on the cards, it allows these exceptions to be rather detailed, since the cards will be easily available for reference during the game.
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