Thursday, November 5, 2009

Use-based Skill Gain, Revisited

My post on the character progression has informed my previous analysis on use-based skill gain. Using the tools I provided in that article, I’d like to re-examine use-based skill gain in more detail and draw some distinctions that I missed last week.

Ryzom vs. Darkfall

We are only concerned with systems that grant XP based on the use of specific abilities within a skill-based system. These systems are called “use-based” because the amount of XP you get towards an ability or ability group depends on how much that ability or an ability within that ability group is performed by the character.

Ryzom and Darkfall illustrate two distinct approaches to use-based skill gain. Here’s how their systems answer the three “scope of experience” questions:

  • What will grant experience?
    • Darkfall: Performing any action to completion.
    • Ryzom: Completing a quest or killing an enemy.
  • What will an experience point apply to?
    • Darkfall: The ability group to which the action belongs that granted it.
    • Ryzom: XP is distributed proportionally to ability groups depending on the abilities used to kill a monster. XP is scaled based on the difference between ability group level and enemy level.
  • What can an experience point be spent on?
    • Darkfall: Only on increasing the level of the skill or skill group to which the experience point applies.
    • Ryzom: XP in an ability group goes towards leveling that ability group. Once the group is leveled, XP is converted into points used to buy new abilities and effects.

Runaway Positive Feedback

Notice how narrow and direct Darkfall’s system is. You get XP that is allocated to what you just did. You can’t specialize in any way beyond what you’ve done because of the narrowness of experience’s scope. If you want to perform well (before you’ve capped all your abilities—the lack of cap really kills specialization at growth’s end), you are stuck using the abilities that you’ve used most. So if you are pushing yourself by trying the most challenging content you have a chance at completing, you are stuck using the same set of abilities to the exclusion of almost all else. The positive feedback loop created in this way does not meet its end until you reach the ability cap. Then, and only then, does an optimal build begin bringing its other abilities up.

The pendulum swings between the necessity of complete specialization during character growth to the complete lack of specialization at growth’s end. I see this as the worst of both worlds. To play optimally, you’re trapped into using only what you’ve spent the most time using—until you’ve maxed everything out, at which point it doesn’t matter.

By broadening what XP can be spent on, a system allows specialization beyond exactly what the character is using. Ryzom’s system benefits significantly from letting players choose what their experience will improve within an ability group, instead of forcing the growth to occur in specific points. The positive feedback loop of growth in a certain area spurring further growth does not disappear, but it is significantly moderated.


A system is more exploitable if the rewarded action is one swing of a sword. If the completed action is broader—like, say, killing an enemy in Ryzom’s system—then the problem largely goes away. Ryzom’s system proportions XP in a use-based fashion, but doesn’t focus all growth only on counting ability use.

The optimal strategy for becoming a master swordsman should not be:

  • Find a friend who can debuff attack power and buff defense.
  • Have him debuff your attack power.
  • Have him buff your defense.
  • Find a mob that has a lot of health.
  • Debuff the mob’s attack power.
  • Buff the mob’s defense.
  • Swing at the mob a million time until it dies.

If that is feasibly the most effective way to gain skill levels, the system is broken. It’s trivially easy to level up that skill. In Ryzom’s system, you can’t gain XP beyond some fixed cap for a given monster, regardless of how many times you swing your sword at it. It’s clearly easier to exploit a use-centric use-based system than it is to exploit a system that rewards only broader accomplishments, like killing an enemy.

Limited Reward Potential

Darkfall has such as strict conception of use that characters cannot be rewarded for any activity above the use of an ability. Why should a system be so restrictive? It cuts out much of the benefit in the experience point abstraction. Ryzom reaps the rewards of using an experience point system while still maintaining the customizability and flavor of a skill-based advancement system.

Use-centric Advancement Systems are Inferior

It’s important that we draw the distinction between use-centric systems, like Darkfall, and other use-based systems. Use-based systems filter XP towards limited ability groups based on what abilities were performed to cause the XP gain. Darkfall’s system represents a pure version of this where use is the center of advancement: all character progress is based directly on use and little else. Systems work better when, like Ryzom’s, use has a more abstract incorporation into how character growth happens.


Brian 'Psychochild' Green said...

I see where you're coming from a lot better now. A more insighful analysis. A few thoughts:

I'm not sure "positive feedback loop" is the term you really want here. I think it's more precise to say that it's easier to use rarely used abilities in an alternative system. In a real game, most people who have a skill that is useful will go practice it; if you have a healing skill, for example, you're not going to wait until you're in the middle of a bad situation to finally use it and hope it saves you.

As for exploiting, I think that part of the issue here is that level-based systems have had more people pounding on them and thus the exploits have been addressed. There's nothing in use-based design that says if you repeatedly hit the same target you'll get skill increases. Just like there's nothing in level-based designs that say you need to get xp for killing very low-level monsters. The concept of trivial monsters ("gray con" that reward no experience) was introduced because people exploited that in gaining levels. Plenty of other exploits still exist; for example, people racing to the top level form AoE grinding groups and just go murder stuff en-masse, gaining lots of xp in a short amount of time.

This side-steps the whole discussion of "what is an exploit", though. Is AoE-grinding really an exploit, even though it allows faster than anticipated advancement?

I guess my driving thought is that few of these issues are intrinsic to every use-based system, no more than AoE grinding or killing level 1 enemies to max level have to be part of every level-based system. You could add elements to the design to "fix" most of these problems just as xp/level-based systems have fixed various problems over the years as well.

So, let's to back to M59's hit point advancement system. It avoids nearly all these problems you point out. You only get a chance to get a hit point upon killing an enemy that is hard enough, so you can't sleaze increases by killing weaklings or trying to hit the same monster repeatedly. Hit points are universal, so there's no worry about specialization ("positive feedback loop"). Hit points could be awarded from other sources like quests; there were temporary hp buffs that were removed because they were buggy, but the rewards could be permanent. This is still, at the core, similar to a use-based system. What are the remaining problems?

Anonymous said...

That's a very interesting analysis, and I agree with most of the problems (the inadvertent snowballing into lopsided stats in particular), but I disagree on the "exploitation" issue. I think the tactic you outline basically turns a battle into training, converting the enemy into a training dummy and dulling and weighting the player's weapon. That sounds really realistic to me.

And with all the talk about grinding this past week (thanks, no doubt, to Dragon Age), I think I find my experience is that greater immersion makes grinds more tolerable for me. Then again, use-centric advancement isn't the final word in realism.