Balance deals with fairness as perceived by players, difficulty, and ensuring that skill (and not chance) is the main factor in player success. Players left-behind should be able to catch up. Stalemates should be avoided because they make some players feel like they played in vain (in other words, better players should always win). No sudden drops or peaks in difficulty. No sudden loss of the game without having previously given the player adequate information about his decisions. Respect genre: no logic puzzle inside a flight simulator.
Avoid dominant strategies
If entities are perfectly balanced and the player can see it obviously from the entities' external stats, then the game looks bland. Therefore, there should be shadow costs. Shadow costs are eventually learned by players after a while if they are not completely hidden. They should not be completely hidden, otherwise the player wonders why his performance fluctuates. More on shadow costs from Ian Schreiber.
Transitive relationships (A>B and B>C implies A>C) are good for player upgrades (sword A gives more atk than sword B). Intransitive relationships (rock paper scissors) are better with unequal costs and gains because players may take risks (and be rewarded for the risks taken). In fact, ideally, all units should be orthogonally different: they should differ in at least 2 dimensions, or have at least one capability that no other unit in the game has. Orthogonally different units prevent dominant strategies because all units are needed to reach the goal. Ex: in Chess, using the Queen only because she's the strongest is a losing strategy.
Chance can be used in frequent low risk and low-reward challenges.
Allow the player to choose how much to risk. Skill is taking the good risks with enough information given: Poker players can decide to lose very little if they have a bad hand this turn: they do not bet much.
Good luck cancels bad luck over time. In the end, skill makes the difference.
Do not use chance for large issues unless the player knowingly takes the risk.
Symmetric PvP games can get boring: players end up using the same strategy. It can be hard for some symmetric games (Go or RTS) to have a non-cheating AI better than humans. Players accept a cheating AI (able to see units in fog of war, faster production, ...) in very hard mode, not in easy. Basically, the game becomes asymmetric when players accept a handicap.
See also Ian Schreiber's game balance class.
At least two factors are outside designer's control. Players have a previous experience acquired by playing similar games of the genre. Players have also a native talent (hand-eye coordination, reasoning, ...). Other factors that the designer can control to adjust the perceived difficulty are: intrinsic skill, stress, power provided and IG experience.
- Absolute difficulty of a challenge = skill + stress required compared to the trivial case (static, harmless, one-shot-killed enemy in an FPS)
- power provided = avatar's strength, subject to feedback loops. Ex: spell, powerful sword, HP, ...
- relative difficulty = absolute difficulty - power provided.
- IG experience = how often the player has been exposed to similar challenges throughout the game.
perceived difficulty = absolute difficulty - power provided - IG experience.
Problem with adaptive difficulty: player may learn to trick the AI in pretending to be bad throughout the game and play well at the very end to crush the AI. Moreover, finding a relevant success metric is sometimes hard. Adaptive difficulty should not be obvious to the player, otherwise it feels like patronizing. Adaptive difficulty can be used to make the game harder for players who choose it, though.
Discourages stalemate and rewards success usefully (not just cosmetically). To control positive feedback,
- Rewards should not be too big
- increase absolute difficulty as player gains rewards, so that relative difficulty stays in control
- allow players to team up against the leader
- make victory conditions unrelated to player power
- use chance to decrease player rewards (random loot, ...)
Stagnation happens when the player does not know what to do because she does not have enough information. Ex: finding a secret exit door hidden somewhere in a Doom level. To avoid stagnation, give hints.
Players should not have to waste time on trivialities (micromanagement) when they want to take higher-level decisions (strategic positioning of armies), unless they ask for it. Ideally, the game should let the player decide the levels she wants to be in charge of. Experts can choose to micromanage.
How to tune easily:
- Factorize mechanics shared by multiple entities,
- Modify one parameter at a time to see its effect,
- To measure the effect of a parameter, double or halve it,
- Keep track of the tuning done so far, so that you do not do the same tweak twice (saves time)