Fluxx

Fluxx is a card game published by Looney Labs in which the rules of play and the conditions for winning are not fixed but change continually during the game. Players alter them by playing cards from their hands, so that the rules in force at any moment are whatever the cards on the table say they are. Because the goal itself can be replaced by a card played mid-game, no two games follow the same course, and the design rewards adapting to shifting conditions rather than mastering one fixed set of rules. The game is published by Looney Labs, and its changing-rules mechanic is its defining feature.