21 March 2011

[Literature] Game Balance ch3 - Transitive Mechanics and Cost Curves

My notes from course 3 of the Game Balance class of Summer 2010, by Ian Schreiber.

An intransitive game is like Rock-Paper-Scissors, where everything is better than something else and there is no single “best” move. In contrast, in transitive games, some elements are just flat out better than others, and we balance that by giving them different costs.

The cost is expressed in terms of game resource(s) (eg money, wood, existing units, items, technology, skills, ...) but can also consist of temporal restrictions (eg single-use constraint on a particular item, or a bonus being limited in time). A player wil pay a cost if she can see benefits to her situation (eg better stats, bonus skill). The goal for the game designer is to reach benefits = cost. In other words, if the weapon is overpowered, then either decrease its power (or any benefit) or increase its price (or any cost). Overpowered <=> undercosted.

A cost curve is a game balance technique designed to put everything in terms of the resource cost. In some games, you can choose to make an increasing, linear or decreasing curve, all of them might be balanced, but they have different effects on the gameplay. In Magic: the Gathering you get one Mana per turn. If you were the designer and you made a cost curve that was increasing, so that each additional point of mana gives you more benefit than the last, you’ll have a game where late-game cards are really powerful and early-game cards are pretty weak, so you’ll have a game that is heavily weighted towards late-game play. If the cost curve is decreasing, it puts more of a focus on the early game. The curve depends on the game duration you expect.

How to build or reverse-engineer a cost curve?

  1. Start with objects that have only one little effect: is their effect cost linear, exponential or log?
  2. then, combine effects; does having +2atk AND +5def in the same item more expensive than having them separately?
  3. then, look at limited or random effects
  4. then, keep in mind the metagame (ex: all goblins in the battlefield get a bonus => full goblin deck gets OP)

"Reverse-engineering" the transitive costs and benefits from an existing game means solving (mostly) linear equations. Ex: 2HP+1atk=5po and 3HP+2atk=10po => Xpo/HP and Ypo/atk. There might be inconsistencies/exceptions for elements "manually" balanced. Creating from scratch a cost curve = intuition + playtesting, then maths with later additions to the game. Guidelines to create a cost-curve:

  • A limited benefit is always worth something.
  • If an item gives the player the choice between benefit X or benefit Y, then the cost of this item is more than the cost of X + the cost of Y. Choice has a price.
  • Too weak is better than too powerful.

There is an "escalation of power" problem for CCG or MMO (mudflation), or any game which elements are persistent. When some elements are slightly overpowered, players find them after a while and these items become the standard. For the next expansion, the cost curve has to raise to adapt to these OP items, and the new set of items is balanced in this new higher curve. It forces players to buy things at each update, but it should not be too obvious, otherwise players will see it and leave the game. => Do it VERY slowly.

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