When designing characters/items, what sort of methods do you use to decide how many abilities or how strong those abilities are when adding them to the design of the kit but before you run internal testing on it?
There's generally two different processes when designing an item or a character - the very first time, when we're still figuring out what an item or character is supposed to be within the context of the game (i.e. prototyping), and all the times after that once we know what the thing we're designing is, so we're just designing another different one (i.e. creating content).
When we're prototyping, there's no real sense of strength because there's nothing to compare against yet. Strength or weakness only exist within a reference point. A weapon dealing 100 points of damage doesn't mean the weapon is strong or weak unless you know that another weapon deals 10,000,000 damage. We're thinking more of what the in-game expectations are - [how long it takes to kill an enemy], how the player attacks, how many different attacks the player has, what effects the player's attacks will have in addition to damage, and so on. The items or enemies we create while prototyping are usually intended to be representative of regular gameplay where the player will spend most of her time, so they won't really skew strong or weak.
Once we're done prototyping and have a good idea for what an item or character is, we establish certain rules and guidelines for creating more of those things. The more systemic the thing is to build, the cheaper and easier it is for us to create more. The more complex the thing is to build, the more expensive and difficult it is to create more. This includes a general budget for each kind of thing we're making. Thus, we can make a large number of minion monsters that pull from a shared pool of abilities, but only have the development time for a handful of involved and scripted boss monsters with a lot of abilities in order to make those experiences memorable.
Whenever we're making a batch of things, we have some number we're aiming to make that's determined by our budget and schedule. We can break this number down into things like archetypes (e.g. light melee, short range, long range, glass cannon, heavy armor, etc.) and then further into individual instances of those archetypes (e.g. goblin raider, goblin slinger, goblin archer, etc.). Then it's just about going down the list to fill out the breadth of play experience. System designers usually try to set up some base formula for power based on how the player measures strength - how long the enemy lives, how much damage the player can take, etc. Those formulas guide the general strength for each thing in the game. As we playtest, we tweak the formula to better model the play experience we want and we can tweak the individual elements (monster, item, ability, etc.) to tailor any specific experiences we're designing for (e.g. boss battles, critical points, etc.).
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