Balance (game design)
In game design, balance is the concept and the practice of tuning a game's rules, usually with the goal of preventing any of its component systems from being ineffective or otherwise undesirable when compared to their peers. An unbalanced system represents wasted development resources at the very least, and at worst can undermine the game's entire ruleset by making important roles or tasks impossible to perform.
Balancing and fairness 
Balancing does not necessarily mean making a game fair. This is particularly true of action games: Jaime Griesemer, design lead at Bungie, said in a lecture to other designers that "every fight in Halo is unfair". This potential for unfairness creates uncertainty, leading to the tension and excitement that action games seek to deliver.
In these cases balancing is instead the management of unfair scenarios, with the ultimate goal of ensuring that all of the strategies which the game intends to support are viable. The extent to which those strategies are equal to one another defines the character of the game in question.
Simulation games can be balanced unfairly in order to be true to life. A wargame may cast the player into the role of a general who was defeated by an overwhelming force, and it is common for the abilities of teams in sports games to mirror those of the real-world teams they represent regardless of the implications for players who pick them.
Difficulty level 
Digital games often allow players to influence their balance by offering a choice of "difficulty levels". These affect how challenging the game is to play.
In addition to altering the game's rules, difficulty levels can be used to alter what content is presented to the player. This usually takes the form of adding or removing challenging location or events, but some games also change their narrative to reward players who play them on higher difficulty levels (Max Payne 2) or end early as punishment for playing on easy (Castlevania).
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).
Difficulty can also be managed by a third party or the game itself; see the Gamemaster section below.
Balancing goals shift dramatically when players are contending with the game's environment and/or non-player characters. Such player versus environment games are usually balanced to tread the fine line of regularly challenging players' abilities without ever producing insurmountable or unfair obstacles. This turns balancing into the management of dramatic structure, generally referred to by game designers as "pacing".
Pacing is also a consideration in competitive games, but the autonomy of players makes it harder to control.
The simplest game balancing technique is giving each player identical resources. Most competitive games feature some level of symmetry; some (such as Pong) are completely symmetric, but those in which players alternate turns (such as Chess) can never achieve total symmetry as one player will always have a first-move advantage.
Statistical analysis 
The brute force approach to balancing is the mathematical analysis of game session results. With enough data, it is possible to identify unbalanced areas of a game and make corrections.
Randomization of starting conditions is a technique common in board games, card games, and also experimental research which fights back against the human tendency to optimise patterns in one's favor.
The downside of randomization is that it takes control away from the player, potentially leading to frustration. Methods of overcoming this include giving the player a selection of random results within which they can optimise (Scrabble, Magic: The Gathering) and making each game session short enough to encourage multiple attempts in one play session (Klondike (solitaire), Strange Adventures in Infinite Space).
Feedback loops 
Many games become more challenging if the player is successful. For instance, real-time strategy games often feature "upkeep", a resource tax that scales with the number of units under a player's control. Team games which challenge players to invade their opponents' territory (football, capture the flag) have a feedback loop by default: the further a player pushes, the more opponents they are likely to face.
Although gamemasters have historically been humans, some videogames now feature AI systems that perform a similar role by monitoring player ability and inferring emotional state from input. Research into biofeedback peripherals is set to greatly improve the accuracy of such systems.
In role-playing game slang, a "gimp" is a character, character class or character ability that is underpowered in the context of the game. Gimped characters lack effectiveness compared to other characters at a similar level of experience. A player may gimp a character by assigning skills and abilities that are inappropriate for the character class, or by developing the character inefficiently. However, this is not always the case, as some characters are purposely "gimped" by the game's developers in order to provide an incentive for raising their level, or, conversely, to give the player an early head-start. An example of this is Final Fantasy's Mystic Knight class, which starts out weak, but is able to become the most powerful class if brought to a very high level. Gimps may also be accidental on the part of the developer, and may require a software patch to rebalance.
Sometimes, especially in MMORPGs, gimp is used as a synonym for nerf to describe a rule modification that weakens the affected target. Unlike the connotatively neutral term nerf, gimp in this usage often implies that the rule change unfairly disadvantages the target.
Among game developers, MMORPG designers are especially likely to nerf aspects of a game in order to maintain game balance. Occasionally a new feature (such as an item, class, or skill) may be made too powerful, too cheap, or too easily obtained to the extent that it unbalances the game system. This is sometimes due to an unforeseen bug or method of using or acquiring the object that was not considered by the developers. The frequency of nerfing and the scale of nerfing vary widely from game to game but almost all massively multiplayer games have engaged in nerfing at some point.
Nerfs in various online games, including Anarchy Online, have spurred in-world protests. Since many items in virtual worlds are sold or traded among players, a nerf may have an outsized impact on the virtual economy. As players respond, the nerf may cause prices to fluctuate before settling down in a different equilibrium. This impact on the economy, along with the original impact of the nerf, can cause large player resentment for even a small change. In particular, in the case of items or abilities which have been nerfed, players can become upset over the perceived wasted efforts in obtaining the now nerfed features.
A well-known instance in which a nerf has caused many protests, but much more praise, is when Infinity Ward nerfed the Model 1887s in its video game Call of Duty: Modern Warfare 2. Before the nerf, the Model 1887s were able to One Shot Kill from medium-long range when all other shotguns in game were limited to short-medium range. The nerfing of the Model 1887s reduced its range to short range.
For games where avatars and items represent significant economic value, this may bring up legal issues over the lost value.
Overpowered (often abbreviated to OP) is a common term referring to a perceived lack of game balance. It is often used when describing a specific class in an RPG, a specific faction in strategic games, or a specific tactic, ability, weapon or unit in various games. For something to be deemed overpowered, it is either the best choice in a disproportionate number of situations (marginalising other choices) and/or excessively hard to counter by the opponent compared to the effort required to use it.
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