# What is the design rationale for having armor and magic penetration mechanics?

It seems to me that the penetration stat found in many games adds needless complexity and often is not easily understood.

It is obvious to a player that if they are taking a lot of damage, then they need to get armor.

An opposing player then has to decide whether or not to get an item to do more damage or an item to do armor penetration.

The answer is often not obvious. The player could look up definitions and statistics on the web and not get a clear answer. They can scour forums and find several different explanations both for and against one or the other.

To me this seems needlessly complex. If more damage can't scale with more armor, then shouldn't damage be buffed or armor be nerfed? Am I missing something obvious?

• A game is a series of meaningful decisions, if they aren't decisions, they aren't meaningful. – Draco18s Oct 6 at 19:01
• It has to be complex, otherwise your player base will quickly "figure it out" and you will have a single build that is superior to others. Well, they will figure it out anyway, but this way it will take longer and will feel more gratifying. – Andrew Savinykh Oct 7 at 5:26
• Consider real life: a hollow point bullet works great against unarmored people, but a Kevlar vest will stop it. Armor piercing bullets, on the other hand, go through Kevlar, but they also pass through flesh dealing relatively minor damage unless a vital organ is hit. There are no golden bullets, the whole point of equipping your units is knowing what opponents will they meet and how precisely they can aim. – Agent_L Oct 7 at 10:20
• If you have armor penetration in the game, doesn't that mean that the decision to get a lot of armor is not obvious? Players taking a lot of damage would need to decide whether it is more efficient to purchase additional life (which is immune to armor penetration) or additional armor (which multiplies your effective life). – Onyz Oct 7 at 15:09
• One side note I don't see mentioned yet is a lot depends on the implementation of the penetration. Different implementations can have different effects on the decision space. Do you have a specific implementation in mind? – Lunin Oct 7 at 22:16

I think there are three aspects of this:

• Meaningful decisions.
• Balance.
• Mechanic complexity.

On the meaningful decisions aspect... well, if the answer to armor is more damage, then that is not a decision. It is good for there to exist multiple ways to deal with a situation. I mean, multiple different in kind (not just in raw numbers) ways. Not simply picking the attack with more dps.

If just more damage is always the answer, then deciding what attack to use is NOT interesting. It might aswell be automatic. There might aswell be a single kind of attack (and unique equipment).

Ideally we would have unique mechanics instead of more stats. However, from the point of view of meaningful decision, the option of bypassing armor is valid.

The answer is often not obvious.

It should not be. From the point of view of balance, if there is one single way that is clearly the best, then the options are not balanced. Au contraire, the use of armor penetration or just more damage should be primordially of preferred game style (and then of tactics and availability).

It also makes sense for there to be ways to counter or avoid armor penetration. It can be something that negates damage, something like evasion (if it makes sense in the game, e.g. turn based tactics) or user agility (if it makes sense in the game, e.g. action rpg), it can be attacking from greater distance, whatever.

To me this seems needlessly complex.

That goes for the particular case of each game, how exactly was the mechanic implemented and what other mechanics it synergy with. Armor penetration can be straight forward: it does this amount of damage ignoring armor. Done.

It can be complex, if the way to counter armor penetration is with armor that have some sort of resistance to armor penetration… then it isn’t really armor penetration, is it? I mean, designer can come up with odd logic for these mechanics.

If the player has to...

look up definitions and statistics on the web

... to be able to use it. Then we have a problem of clarity. The mechanics are not clear, not easy to understand. It could be that the mechanics should be reevaluated, or it could be just a matter of better UI (if it is not that bad), in fact if the UI designers or the writers are having trouble explaining the mechanic, the game designers probably should have another look at it.

On the other hand, if the player has to...

look up definitions and statistics on the web

To decide which is better, despite both using armor penetration and more damage (and hopefully other options) being perfectly viable options and easy to use... we have an optimizer player. It is good to have of those. And it is good to have mechanical depth for them. There is people who enjoy figuring out that stuff. There is people who take pride in having or using the optimal solution.

Also, web sites, video explanations, wikis, forums, and other online communities spawning around the game are a good thing.

If more damage cant scale with more armor, then shouldnt damage be buffed or armor be nerfed?

Buffs and nerfs are often not trivial. You need to consider other mechanics. Is there a mechanic that reduces armor? What about one that deals damage overtime? Are there invulnerability mechanics? etc...

While it is true that developers can create a mess, perhaps by good old accretion. That does not mean that armor penetration by itself is a bad design.

It could be it is a bad idea in whatever game you had in mind when writing the question, it does not mean it is in general.

• Good answer, but you might include the formal term for what you're describing, so the OP can search for more info: Asymmetric Game Design – MandisaW Oct 6 at 16:56

For fun.

Let's consider the most simple mechanic available: a character has N points of Health, and always does 1 point of Damage per Second. When two characters fight, the one with the most points of Health at the start of the fight wins. Done.

Would this be fun? I, personally, would not find it very fun.

In RPG/FPS games where these mechanics come into play, players invest time, and wish for their experience and skill to distinguish them. That is the fun that they are looking for.

In order for experience/skill to matter, the player needs to have meaningful choices at their disposal, which in turn means that the player should be facing a variety of situations and the best choice should differ based on the situation. If the best choice is always the same, there is no meaningful choice to be made, and therefore no way to show off the experience acquired or the player's skill.

In order to create such a variety of situations for the players to enjoy, game creators will therefore create multiple (competing) mechanics such as distinguishing between Health and Armor. Even a rudimentary choice between two attacks High Damage/Reduced by Armor vs Medium Damage/Bypassing Armor will require the player to make a timely choice based on the target: a low-armored target is best dealt with the former, a highly-armored target with the latter... and a medium-armored target will require some experimentation, and thus experience.

As a player, though, I would not agonize over the exact threshold at which one attack is better than the other. If a statistical analysis is required to figure it out, after all, it likely means that the difference is slim enough not to matter that much in practice, and other factors will have more impact.

• And in most cases, the one that uses the least MP will be the de facto best choice anyways, since RPG players are notoriously stingy with resources outside of boss fights. ;P – Justin Time 2 Reinstate Monica Oct 6 at 19:26
• @JustinTime, ...because RPGs are notoriously stingy about providing resources. – Mark Oct 6 at 20:35
• @JustinTime: Depends on context. Grinding => Marathon => aim for efficiency; PvP => Sprint => aim for maximum damage :) – Matthieu M. Oct 7 at 14:34
• That's fair, on both counts, OP and @Mark. I was just making a tongue-in-cheek reference to the "too awesome to use" hoarding mentality. ;P – Justin Time 2 Reinstate Monica Oct 7 at 16:04

Games often benefit from having soft counters in them. You might have a situation where you want some people to have good DPS against armored targets, while other people have good DPS against healthy targets, but let people increase their damage or armor penetration in response to whether they feel they need to do better against armored targets or against healthy targets.

The math for armor penetration is, in all but the simplest of cases, going to end up at least one step more complicated than the math for how armor works.

Let's take League of Legends for example:

If Armor >= 0: damage multiplier = 100/(100+Armor)


So Armor 100 makes you take 50% damage, and Armor 300 makes you take 25% damage. Armor penetration makes you treat the armor as though it were lower, so if you have 50% Armor Penetration, you deal 67% damage to someone with 100 Armor (that's equal in value to +33% damage), and you deal 40% damage to someone with 300 Armor (that's equal in value to +60% damage). It's not that complicated in principle, there aren't that many elements you could take away to simplify it, and yet the math needed to determine whether going for +10% Armor Penetration or +15% Damage would be a better deal against each of your five opponents is more than most people can do in the heat of a match.

• 100/(100+Armor/100) should be 100/((100+Armor)/100), or even better: 1/(1+Armor/100) – Gábor Fekete Oct 7 at 13:48
• Oh, looks like I did make a typo when quoting the league of legends wiki. – Foxwarrior Oct 7 at 17:05

[For this post, whenever the mechanical implementation of attacks is relevant, they are assumed to have a fixed damage component, a random damage component, one or more stat-based components (either multipliers and/or bonuses), and a penetration component (either flat value or percentage). Armour's lower bound is clamped at 0; even with penetration, it can never be negative; it is also capped, with an unspecified upper bound.]

Apart from the decision and balance issues, armour penetration is secretly one of the most flexible tools you have as a developer, and can be used as the underlying implementation of a lot of seemingly-unrelated mechanics. [I won't say whether it should or not, because that typically depends on the amount of complexity you want, and how much interaction you want there to be between said seemingly-unrelated mechanics. In particular, this becomes less viable if you want different effects to apply their own multipliers, and more viable if you want them to all influence a single, stacking multiplier.]

For a short list, let's look at...

• Critical hits: Generally, crits increase the damage dealt by an attack. This is usually accomplished by a damage multiplier, but can also be implemented as "ignores [some/all] defense"; in particular, "ignores [some/all] defense" is a good, logical mechanism for stabbing/piercing weapon crits, on the assumption that you actually are poking through one of the little openings in their armour.

• Fixed damage: Fixed damage attacks by definition ignore armour. If you have an armour penetration mechanic, then you can use it to trivially implement a fixed-damage attack: Set the random and stat-based components to zero, and the penetration to maximum (either 100% penetration or equal to the armour cap).

• "Flat-footed" or "Touch AC" mechanics: If familiar with 3.5e or PF, you may be familiar with these; they're both different flavours of armour penetration. [If not familiar with them, D&D and related games combine your armour and your evasion as your AC (Armor Class, generally equal to 10 plus any relevant bonuses), with 3.5e and Pathfinder in particular having a mechanic that turns off the evasion half (if flat-footed, you don't add your Dex bonus to AC) and one that turns off the armour half (touch AC doesn't include your armour/shield/natural armour bonuses); e.g., if you have +2 Dex, and armour that gives +3 AC, then you have 15 AC normally, 13 AC if flat-footed, and a touch AC of 12.]

While both of these would need special handling to determine how much of your AC they remove, the amount can just be plugged into your armour penetration mechanic once it's calculated.

• This can also be used for broader "Bypass Armour" mechanics, which can typically be implemented as "set armour penetration to maximum" unless you need finer-tuned control. [In cases where you need fine-tuned control, it would likely be because you want to distinguish between different types of armour, in which case it would work similarly to flat-footed vs. touch AC.]
• Elemental weakness/resistance: In some games, this can be implemented as a weakness multiplier applied to your damage, typically something like 1.5x for weaknesses and 0.75x or 0.5x for resistances. An alternate means of implementing it would be to have weakness and resistance increase and decrease a percentage-multiplier penetration value.

There are likely other effects that could be implemented to rely on armour penetration as well, but none come to mind at the moment. Of course, each of these effects could also be a separate multiplier and/or bonus, representing a distinct step in the damage formula. It all comes down to how you want your game to work, really.

Apart from other reasons it might be dependant on whether the game wishes to simulate a certain (very limited usually) amount of realism. For example, a game I played quite some time ago, (a MUD in fantasy setting), had the armour and melee weapons available to players, which all had base stats and modifiers for different standard damage types: slash/impale/bludgeon.

Therefore a plate mail armour would be quite resistant to slash (slashing swords, axes), also rather resistant to impale (lances and rapiers) and weak against bludgeon - maces, hammers, etc. - damage.

When fighting other players and NPCs it was sometime useful to switch weapons or wear different kinds of armour.

In practice, however, the advantage was frequently nullified by the base stat of the piece, when the modifiers were small.

The easiest example to illustrate that the choice between AP and raw damage is a situation in which there is more than one opponent and the player cannot change the gear option between fighting multiple opponents.

Now the player has a choice. Specialize in defeating the armored opponent, and do less effective damage per attack to the unarmored ones, or specialize in dealing damage to the squishies and do less effective damage per attack to the tanky opponent.

Now regardless of the mathematical complication, or the min/max behavior of the player, or the genre of the game, or many other variables, this decision adds value to the gameplay.

If more damage cant scale with more armor, then shouldn't damage be buffed or armor be nerfed?

Then there's only one dimension. Every unit can be ranked from better to worse on that scale, and there's no reason to use any but the best unit. One major part of making a game interesting is nontransitivity: Unit A can best Unit B which can beat Unit C which can beat Unit A. One way of doing this is through armor. Unit A has high basic attack and no armor. B has medium basic attack, but high armor penetration. C has high armor and low attack. When A fights B, B has no armor to stop the high attack, and B's penetration is useless since A doesn't have any armor. When B fights C, B's penetration counters C's armor. When C fights A, C's armor stops A's attack.

To me this seems needlessly complex.

Depends on what you consider "needless". If you want the game to just be about getting the strongest character, then yeah. But if you to have different character types that all have a situation where they're useful, then this sort of thing is needed.

The player could look up definitions and statistics on the web and not get a clear answer. They can scour forums and find several different explanations both for and against one or the other.

It's not quite clear as to whether you're presenting an issue regarding documentation about the base rules, or availability of higher level strategy. If the effect of armor isn't available in-game, that is an issue of documentation, rather than the mechanism itself. If the rules about what armor and armor penetration are clearly available, but it takes a lot of analysis to decide how useful they are, that's part of playing the game. For instance, if someone's explaining chess, they should mention that bishops move on diagonals and can't jump over pieces, while knights move in L-shapes and can jump over pieces. That's the basic level of the mechanics. There are higher levels, such as "if a bishop starts on a particular color, then it can't move onto the other color", "you can pin pieces with a bishop, but not with a knight", or "it's easier to fork pieces with a knight than with a bishop" that aren't explicitly part of the rules, but are consequences of them, and are part of learning chess strategy. Then there's even higher level facts such as "bishops are generally more valuable than knights" that are going to have a lot of exceptions (this is less true during the opening) that take a lot of mastery to apply, and there's going to be disagreements as to when they apply. If "trading a knight for a bishop is good" were always true, then that would take strategic depth away from chess.