narrative to reward players who play them on higher difficulty levels or end early as punishment for playing on easy. Difficulty selection is not always presented bluntly, particularly in competitive games where all players are affected equally, and the standard "easy/hard" terminology no longer applies. Sometimes veiled language is used (Mario Kart offers "CC select"), while at other times there may be an array of granular settings instead of an overarching difficulty option. An alternative approach to difficulty levels is catering to players of all abilities at the same time, a technique that has been called "subjective difficulty". This requires a game to provide multiple solutions or routes, each offering challenges appropriate to players of different skill levels (Super Mario Galaxy, Sonic Generations). Feedback While tester feedback is important when developing and updating a game, there are certain things to be kept in mind: Skill and the ability to explain do not necessarily correlate with each other. There are typically more players than developers, so they are better at solving it. Additionally, new tester should be added from time to time since practice effects emerge. Gamemaster A game can be balanced dynamically by a gamemaster who observes players and adjusts the game in response to their actions, emotional state, etc, or even proactively changes the direction of the game to create certain experiences. Although gamemasters have historically been humans, some videogames now feature artificial intelligence (AI) systems that perform a similar role by monitoring player ability and inferring emotional state from input. Such systems are often referred to as having dynamic difficulty. One notable example is Left 4 Dead and its sequel Left 4 Dead 2, cooperative games that have the players fight through hordes of zombie-like creatures including unique creatures with special abilities. Both games use an AI Director which not only generates random events but tries to create tension and fear by spawning-in creatures to specific rule sets based on how players are progressing, specifically penalizing players through more difficult challenges for not working together. Research into biofeedback peripherals is set to greatly improve the accuracy of such systems. Game theory Game theory focuses more on theoretical modeling of competing players and their decision making and therefore is only for limited use in game design. However, it does offer knowledge and tools like a Net Payoff Matrix that can be helpful to measure power and understand player reasoning.