Determining attack difficulty: what is the best method?

I don't understand why you think you can't find a system that compares attacker and defender stats. You listed one, the most popular RPG ever: D&D(most editions).

Perhaps it will be easier to recognize if I reframe it for you: in D&D, the difficulty of an attack is 10+defender's defensive statistics-your attacking statistics.

I personally think that everything except #4, attack and defense both matter, makes it a waste of page space to base a 'combat' system on. Don't have rules for something your game can only do poorly.

I think that D&D actually is a mixed method.

Your target is solely the AC of the defender - but your roll includes your attack bonus.

Attack vs. defense can be seen as an equation - and as with any equation, you can move things to the left or to the right.

All of the following "equations" are exactly the same:

base attack + strength-bonus + d20 <=> 10 + dex-bonus + armor-bonus

strength-bonus + d20 <=> 10 + dex-bonus + armor-bonus - base attack

d20 <=> 10 + dex-bonus armor-bonus - base attack - strength-bonus

d20 - 10 <=> dex-bonus armor-bonus - base attack - strength-bonus

etc.

If the left side is bigger, it's a hit. If the right side is bigger it's a miss. You can even move the die to the other side - doesn't change a thing.

What I am trying to say is - it does not matter which side of the equation stuff is on. The only thing that matters is, what things are in the equation, and which are not.

The target (= right sight of the equation) doesn't have to include any stat from the attacker. As long as an attacker stat is present in the equation it is "mixed" - as in the comparison of attacker and defender stats both influence the outcome/are being compared.

White Wolf games (at least the old ones I've played) used contested rolls for attack - I roll my attack skill, you roll your defense skill. If I win the contest, damage happens.^1

Attack skills were usually determined by the weapon: melee, archery, martial arts, etc. Defenses were generally dodge (it's own skill, works for nearly any attack) and parry (uses weapon skill, works for some attacks)

^1 (well, a second contested roll happens, based on my damage roll compared to your soak roll. But you could skip this part if it's too much rolling).

There's also the possibility that you always hit-- only the amount of damage or type of effect is in question.

Another option: opposed rolls.

Our homebrew does attacker+skill vs. defender+defenseValue.

And for a given weapon/user damage is proportional to the difference in the rolls, so we get both to-hit and damage with a single opposed roll.

We have different defense values for choosing to try to avoiding parry, armor, etc.... yes, that's cinematic rather than realistic.

Forget about how individual games work. What you need to know is that players think a 60-80% chance of success feels like 50/50 odds.

Games that fall below 60% feel difficult, while those that go above 80% feel unsatisfyingly easy.

A common term for what you seek is "active defense".

GURPS

There are also hybrid systems.

In my game there is a target defense to hit, but in melee combatants roll at the same time as opposed rolls.

I know you are discussing rpgs, but take a look at Imperial Assault, a board game. It does what I think you are asking.

When attacking, you roll different custom dice based on your weapon + abilities. This gives you range, attack damage, and possible special abilities. At the same time, the defender rolls as well. They roll one of two types of dice (signifying hard to kill/hard to hit) - and you compare. So you might roll 4 dmg, 3 range, and a special ability. The defender rolls 2 armor and negates your special. So if you are within range, you deal 2 damage to them.

Hope that helps :)
Justin

THAC0 was Attacker/Defender abilities

Like others have said, DnD is a mix of Attack and Defend and Defender Ability. That always kinda bothered me so in my proto-game, Mythica, I made my own system;

Attack-Defense=Damage. Each weapon has its own Attack Die (Knives are a d6 while an axe is a d10, etc.) and you add the appropriate stat. Meanwhile, Reactions such as Dodge have a d4, Improved Dodge has a 6d, Shields use a d8, Parry depends on the weapon you're using, and so on. So someone with a longsword is very likely to hit some newbie trying to dodge out of the way, but since its the roll of the dice there is always the chance the attack completely misses. The flat bonus that you get from Stats can act as a soft barrier (If you're fighting a master assassin with +10 or more Agility, you're probably going to want to hold off on that fight, or consider some alternative tactics like magicks or explosives.)

The other reason I did this is because it never made sense to me that Attack and Damage is completely separate. Thats why this system is built so that damage is dependent on how strong your attack is vs how weak their defense is.

The first thing you need to do is actually take it back a step and consider what type of story you want your games to tell. Before you decide how to hit a dude in the face, you need to determine how easy it is to murder a guy by way of face hitting.

Are your PCs weaklings like in call of c'thulu? You don't want them hitting every time and one shooting eldritch horrors, so you pick a system that allows that.

Are your PCs average if not slightly above average humans like in Shadowrun? You want average chance to hit but high damage because getting shot or impaled hurts even if your skill in shooting and impaling is on par with your enemy.

Are your PCs heroes like in D&D? You want them to scale up so that at first they are only slightly better than random encounters, but later can AOE them down without effort.

Are your PCs monsters compared to the common folk like in chronicles of darkness? Pick a system where if they pick a fight with a non-combatant then they are just rolling to see how hard they win, not if they win. Then have it so only fighting other superhumans has a chance of failure.

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My game is going for somewhere between Heroes and Monsters, so attackers have a fixed to-hit number and defenders roll to not get hit. Monster stat blocks will always show the maximum defense that can be rolled, so the GM can just speed up combat by knowing some monsters are just meat shields who can't physically block/dodge so he doesn't need to waste time rolling

Shadowrun falls into 4. Attacker rolls dice equal to their attack pool and the defender rolls their defence pool. If the attacker has more successes than the defender the attack lands.

In fact #2 may be the tough one to find as other people have pointed out your only example for that is actually just an example of 4.

[deleted]

In the homebrew RPG that I am writing (a d100, roll under system); it uses an attack rating target, which I arbitrarily chose the base for all characters, is 25%. When you make an attack, roll a d100. To determine a hit, check that your result is less than or equal to your attack rating.

Your attack rating is modified by your skill level with the chosen weapon. If, for example, you have a 50 in the Bladed Weapon skill (which maps to a bonus of +30% in my game), your attack rating with swords, daggers, etc would be 55% (base + skill bonus).

I hope that helps in someway!

I think the reason you can't find straight-up comparing ability values is that there would be no tension. If you have a higher number than the other guy, you win every time. There's no other outcome that can happen. This is why dice rolling is usually involved somewhere.

My game, Sigma, has the player roll one die per aspect of their character that aids them, and adds a number if they're acting in harmony with a belief they hold. This result is compared to a target number that comes from the thing they're attacking (for example). A successful attack adds "progress" which reduces the target for future tests. To overcome the other guy, you have to roll 3 over the target; so as you chip away, it becomes easier to "crit" like that.

I'll tell you what I do in my game (Sword of Virtues) which I (naturally) think is the best method:

Hitting the goblin is a contest between your combat skill and theirs.

You roll 3D6 + your combat skill.

By default, the Goblin's defense score is 10+ their combat skill.

My game uses an Action Point system, so you can do more than one thing in a round. The Goblin has these three options:

1. Defend Passively. That's no action. The target to hit them is 10+ their skill.
2. Dodge: this takes 2 AP (where a full action is 4 AP). The target to hit goes up by 2, so 12+skill
3. React back: this takes 4 AP (meaning it's a full action). The Goblin rolls their skill, you roll yours. Whoever rolls highest hits.

That seems to work well to cover most options for basic combat in my opinion.

Fixed difficulty.

I honestly don't see any significant improvement in the game from making an attack less likely to contact. I think it's better game design to focus your time on robust defense responses and critical effects than the simple act of hitting or missing because that's not really that interesting.

- They are chaosium basic system approach :

The attacker has fixed attack skill, and roll under, then defender has fixed defense skill (parry or dodge) and roll under to avoid damage (or reduce damage from his weapon armor with parry). The are minor rules based on the quality of the success.

There is a variant where attacker can self impose a difficulty, that will be applied both to the attacker and defender (when your opponent is too good a defending, you will use feints and harder attacks)

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My only concern with this one is the multiplication of rolls each turn.

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- And the Rolemaster has a strategic approach to distribute each turn your attack skill points between Offensive and Defensive pools: Attack result = 1d00 + attacker offensive pool - defender defensive pool, the result is compared to a table based on weapon type /Armor type axis, so find the final result (hit, damage, critical effects)

I like this one as it allows the players to adapt their stance to the danger of the situation. (and there is a bit of a secret decision at the beginning of each turn)

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